Embed Size (px)
Citation preview
1
INTRODUCTION:
AMPLITUDE MODULATION BROADCAST SYSTEM
Everybody knows that signal from radio receivers come from radio broadcast
transmitters. What is the composition of an AM broadcast transmitter? How does it form
a radio signal and eventually transmit it?
1. Amplitude Modulation
Modulation – is the process of impressing intelligence on the carrier
Intelligence – signal which contains information
* could be voice, music, code, video, data, etc.
Carrier – wave of constant amplitude, frequency and phase; usually RF
Fig. 1a RF signal (carrier)
Fig. 1b AF signal (intelligence)
Fig. 1c Amplitude Modulated Wave
Figure 1 Amplitude Modulated signal
• in amplitude modulation, the amplitude of the carrier is varied by the intelligence,
the result is an AM (amplitude modulation) wave
• in a AM wave, the envelop of the carrier contains component similar to the
waveform of the intelligence
Figure 2 The modulator combines the RF and audio signals
2
• heterodyning is inherent in amplitude modulation
• heterodyning – process of mixing 2 signals of different frequencies to produce
beat frequencies
a. the sum is called upper sideband (USB) frequency
b. the difference is called the lower sideband (LSB) frequency
• in an AM wave, only the sidebands contain the intelligence
• in AM transmission, the AF signal itself is not transmitted
Figure 3 How signals combine in a modulator
Figure 4 Carrier wave and associated sideband frequencies
Bandwidth
• bandwidth of an AM wave depends upon the frequency of the modulating signal
• bandwidth is equal to twice the highest modulating frequency
Formula: BW = 2 x fa Where: BW is the bandwidth
fa is frequency of modulating signal
Example: fa = 5Khz
BW = 2 x 5 Khz
= 10Khz
Sidebands Power
• transmitter is normally rated according to the amount of unmodulated power and
is called authorized power
• sideband power generated by modulation is in addition to the unmodulated power
• at 100% modulation, sideband power is 50% of the unmodulated carrier power
• at 50% modulation, sideband power is 25%of the amount obtained at 100%
modulation
3
• at 100% modulation, the following condition exist:
a. power in each sideband is ½ of audio modulating power
b. power in each sideband is 1/6 of total transmitter power
c. total sideband power is 1/3 of total transmitter power
d. total sideband power is 1/2of modulated carrier power
• at any percent of modulation, formula below is used in determining power
distribution
Formula: Pt = Pc (1 +m2/2) where: Pt is total transmitter
power
Pc is carrier power
M is modulation factor
Percentage of Modulation
Formula: % of M = es x 100 where es is peak value of modulated
e carr signal e carr and is peak value of
modulated carrier
Example: es = 1000V
E carr = 1250V
% of M = 1000 V x 100
1250 V
= 0.8x100
= 80%
• the higher the percentage of modulation, the greater the power in the sideband
• the greater the sideband power, the stronger the signal received at the receiving
end
• at 100%modulation,maximum possible RF power is produced
• over 100% modulation, distortion and interference are produced
• at 100%modulation,sidebandppoweris 50% of unmodulated carrier power
• at 50%modulation,sideband poweris25% of the amount obtained at 100%
modulation
Figure 5 Percentage Modulation
4
Figure 6 RF carrier showing 50% modulation
Figure 7 Block diagram of an AM radiotelephone transmitter
2. Block diagram of an AM radiotelephone transmitter
RF Section
• generates and amplifies, RF carrier
• consist of Oscillator, Buffer amplifier, and Power Amplifier
AF Section
• generates and amplifiers AF signal (intelligence)
• consists of Microphone, speech amplifier, driver and Modulator
Operations:
Oscillator
• generates RF carrier
Buffer amplifier
• amplifies Oscillator output
• isolates Oscillator from the load
Power Amplifier
• amplifies RF signal further
• couple signal 1 to antenna
5
Antenna
• radiates RF signal in a form of electromagnetic wave
Microphone
• convert sound signal to electrical signal
Speech amplifier
• amplifies Microphone output
Driver
• amplifies speech amplifier output to a level enough to operate the modulator
Modulator
• combine the AF signal to the RF signal
Power source
• provides power for both AF and RF section
FREQUENCY MODULATION BROADCAST SYSTEM
FM system is quite different from AM system. How? and have you ever wondered
why FM reception is superior to AM reception?
3. Frequency Modulation
Concept and terms:
• in frequency modulation, the frequency of the carrier is varied by the intelligence
• amplitude of the carrier remains constant
Figure 8 Frequency Modulated Signal
Figure 9 Bandwidth of FM channel
6
• center or resting frequency – frequency of the unmodulated carrier
• frequency deviation or shift – change in frequency of the carrier from the center
frequency caused by the modulating signal
• frequency deviation is directly proportional to the amplitude of the modulating
signal
• the stronger the modulating signal, the higher the frequency deviation
• rate of frequency deviation is directly proportional to the frequency of the
modulating signal
• the higher the frequency of the modulating signal, the faster is the rate of
frequency deviation
• at 100% modulation, frequency deviation is ± 75 Khz from center frequency
• frequency deviation limits – limits of frequency shift on either side or center
• modulating index – ratio of the maximum deviation to the maximum frequency of
the modulating signal
Formula : modulating index = maximum frequency deviation
maximum frequency of modulating
signal
Example: max. freq. deviation = 60 Khz
Max. freq. of mod. Signal = 15Khz
modulating index = 60 Khz
15 Khz
= 4
• in FM, the maximum allowable frequency deviation is 75 Khz
• highest required frequency of modulating signal is 15 Khz
• deviation ratio – ratio of maximum allowable frequency deviation to the highest
modulating frequency
Formula: deviation ratio = maximum allowable frequency deviation
highest modulating frequency
Example: max. allow. freq. deviation = 75 Khz
highest mod. Freq. = 15 Khz
deviation ratio = 75 Khz
15 Khz
= 5
• deviation ratio and modulation index have the same value only when maximum
deviation results from the highest modulating frequency
• in FM, transmitter operates at maximum efficiency constantly
• it also supplies a constant power to the antenna regardless of the degree of
modulation
• at 50% modulation, frequency deviation is ± 37.5 Khz
Sidebands and bandwidth
• in FM, sideband pair are generated during modulation
• the 1st sideband pair is that of the carrier frequency ± the modulating frequency
• other sideband pair appear at each multiple of the modulating frequency
• guard band – an additional ± 25 Khz beyond the limits of maximum deviation
• total bandwidth including the guard band is 200 Khz
7
Figure 10 Block diagram of an FM transmitter using reactance tube
Modulator and an AFC system
Functions:
Microphone
• converts sound to electrical signal
Speech amplifier
• amplifies Microphone output
Reactance Tube Modulator
• varies the frequency of the oscillator
Oscillator
• generates RF carrier
Frequency Multipliers
• raises oscillator output frequency to the desired value
Power Amplifier
• amplifier RF signal to the desired level
• couples RF signal to the antenna
Antenna
• radiates RF signal in the form of electromagnetic wave
AFC (Automatic Frequency Control) system
• maintains oscillator frequency at correct value during the absence of modulating
signal
• above system is direct FM or crosby system of producing frequency modulation
• power delivered to the antenna remains constant with or without the presence of
modulation
• antenna is horizontally polarized and produces gain
4. FM Boradcast Technical Standards
a. Frequency range 88 Mhz – 108 Mhz
b. Modulating Signal Frequency 20 Hz – 15 Khz
c. IF (Intermediate Frequency 10.7 Mhz
d. Bandwidth 200 Khz
e. Guard band ± 25 Khz
f. Frequency deviation ± 75 Khz
g. Number of station 100 station
8
ANTENNA AND RADIO PROPAGATION
Introduction
No radio system is possible without an antenna. This shows us the importance of
the antenna. This is true whether it is simple radio system or a high-tech radio system.
How does an antenna work? What is the composition of a radio wave?
Presentation
Antenna –wire conductor or conductor in some form that transmits or receives or
both transmits or receives radio wave.
• in a radio transmitter, it is used to radiate radio waves
• in a radio receiver, it is used to intercept radio waves
• in a radio transceiver, it is used to radiate and intercept radio waves alternately
Radio Transmitter Radio Receiver
Figure 11 Radio Transceiver
Fundamental Concepts
• RF current flowing in a wire of finite length produces an electromagnetic field
• EM field may be disengaged from the wire and set free in space
• Moving electric or magnetic field and vice versa in a conductor or free space
• Created electric or magnetic field is in phase in time with its parent field but
perpendicular to it in space.
• Both electric and magnetic field are perpendicular to the direction of motion
• Velocity of radio waves in free space is 186,000 miles per second or 300,000
kilometers per second
• Wavelength and frequency are inversely proportional to each other
Basic Formula: Lambda = velocity over frequency or lambda = 300/f
9
Figure 12 Instantaneous cross section of a radio wave
Where lambda is wavelength in meters and f is frequency in megahertz
Ex1: frequency = 100 Mhz
Sol’n: lambda = 300 / 100Mhz
lambda = 3 meters
Ex2: lambda = 2 meters
Sol’n: frequency = 300 / 2 meters
frequency = 150 Mhz
A. Magnetic Field B. Electric Field
Figure 13 Instantaneous field around in antenna
10
Detachment of radio waves from antenna
• charges producing electric field moves constantly
• movement is from 1 end of antenna to the other as polarity changes
• at 1 instant, antenna is nearly discharged
• charges approach each other, they seem to disappear and their flux lines also
disappear
• detached radiated field is forced away from the antenna at the speed of light
Figure 14 Creation of electric flux lines on a half-wave antenna
Figure15 Distribution Curve of Electrons
Reception
• radiated electromagnetic waves (radio waves) are intercepted by receiving
antenna
• intercepted waves set electrons in motion of conductor (antenna)
• electrons in motion constitute current
• induced current is of small magnitude if receiving antenna is located at a distant
location from the transmitting antenna
• receiving and transmitting antenna have the same general characteristics
11
Radio Wave Components
1. Ground Wave – part of the radio wave that travels along the earth’s surface
and does not use the effects of the ionosphere.
o consists of:
a. surface wave – part which travels along the earth’s surface
b. space wave – part which travels immediately above the earth’s surface
b.1. direct wave – travels directly from transmitter to receiver
b.2. ground reflected – reaches receiver after being reflected from
ground
2. Sky wave – part of radio wave that moves upward and outward and not in
contact with ground
Figure 16 Possible Routes of Ground Waves
Figure 17 Formation of the Ground and Sky Wave
12
Ground Waves.
1. In 1887, Henrich Hertz demonstrated that electromagnetic energy could be sent out
into space in the form of radio waves. Radio waves travel at the speed of light in free
space, 186,000 miles per second, or 300,000,000 meters per second. Free space implies
that radio waves travel through empty space or a vacuum. In actual practice, radio
energy travels slightly slower because of the presence of trees, hills, lakes, and the air it
travels through. If we have a radio frequency of 1,000,000 cycles (1 MHz) per second, its
full wave length is 984 feet. We will use the Greek letter lambda to represent wave
length. V (velocity) will represent the speed of radio waves. F (frequency) represents the assigned frequency.
= V/F
Since: = V/F = 300,000,000 meters per second/1,000,000 HZ (1MHz)
= 300 meters = one wave length one meter equals 3.2808 feet converting into feet
= 300 X 3.2808 = 984 feet = one wave length = then one half wave length /2
= 984/2 = 492 feet
Figure 18 Simple radio communication system.
2. The Atmosphere. How do radio waves travel from the transmitter to the receiver?
What effect does the atmosphere have on our radio energy? The answers to these and
other questions will be answered as we discuss each facet of wave propagation. The
atmosphere around us changes seasonally, yearly, daily, and hourly. The atmosphere is comprised of the troposphere, stratosphere, and the ionosphere.
a. The Troposphere. The troposphere lies from the earth's surface to a height of approximately 6.8 miles.
b. The Stratosphere. The stratosphere lies between the troposphere and the
ionosphere. It is also called the isothermal region. Its height is from 6.8 miles to 30 miles above the earth.
c. The Ionosphere. Because it is the furthest layer away, it is ionized the most by the
sun. It extends from approximately 30 to 250 miles above the earth. The ionosphere has several layers which have varying levels of ionization.
13
3. Frequency Classifications. Not only does each atmospheric layer vary in ionization
levels, but certain bands of frequencies have unique propagation characteristics. The
lower frequencies have different characteristics from the upper frequencies. It is
important to understand how each band of frequencies travels from the transmitter to
the receiver.
Table1. Frequency band coverage.
*1kHz = 1 kilohertz = 1,000 hertz or 1 kHz
**1MHz = 1 megahertz = 1,000,000 hertz or 1 MHz or 1,000 kHz
***1GHz = 1 gegahertz = 1,000,000,000 hertz or 1 GHz or 1,000 MHz
Table 2. Frequency band characteristics.
4. Propagation in the atmosphere. There are two ways radio energy travels from the
transmitter to the receiver: by means of ground waves or by sky waves. The ground
waves travel along the surface of the earth. The sky wave travels from the transmitter to
one of the ionospheric layers and is returned to earth. Long distance radio
communication, depending on the frequency, can be by either ground or sky wave. The
advantage of sky wave communication is that very little power is needed to travel long
distances, say around 8,000 miles. In order to communicate by ground waves, a
powerful transmitter is needed in order for the radio waves to travel the same distances.
A combination of both ground and sky wave communication usually occurs. The earth's
surface affects the radio energy coming in contact with it. Terrain features (jungle,
desert, and large bodies of water) either aid or lessen the radio signal. Diffraction is the
bending of the radio wave with the curvature of the earth. The only variable in a ground
wave signal is the terrain over which it travels. There are many variables in a sky wave
signal: the frequency, the ionospheric layers, the time of day, the season, and the
sunspot cycle.
14
Figure 19 Principal paths of radio waves.
a. Reflection. A radio wave may be reflected. An example of reflection is shown in figure
20. A beam of light is shown into a mirror, almost all of the light energy is reflected. A
radio signal is the same. Depending on the type of surface it contacts, the Signal will be
either absorbed or reflected. Metal surfaces and bodies of water are good reflectors.
Dense vegetation like that found in a jungle will absorb the majority of the radio energy.
Notice in figure 20 that the beam of light is reflected at the same angle it entered the mirror. This is also true with a radio wave reflecting off the earth's surface.
Figure 20 Mirror Reflections
b. Refraction. A radio signal that strikes an ionospheric layer is similar to the wave in
figure 21. When a beam of light strikes a pool of water, the beam is bent slightly. This is
what happens to a radio wave when it strikes an ionospheric layer. The signal is bent and is returned to earth. The terms reflection and refraction are used interchangeably.
15
Figure 21 Bending of light by refraction.
c. Diffraction. If that same beam of light is shown on an object, it will not cast a perfect
shadow. The light rays tend to bend around the object and decrease the size of the
shadow. This also happens to a radio wave that strikes an object such as a mountain.
The radio wave tends to bend around the object. This is shown in figure 22.
Figure 22 Diffraction of wave around solid object.
16
5. Types of Ground Waves.
a. Radio waves that do not make use of the ionosphere are called ground waves. The
received signal strength depends on how powerful the transmitter is. Terrain features the
wave must travel over affects the received signal strength. The Earth's surface reduces
the range of a ground wave signal. Mountains and jungles are bad terrain features. Sea
water is the best terrain feature to transmit a radio signal over. Other bodies of water are also good, but not as good as sea water.
b. Figure 23 shows the various types of ground waves that a radio signal may take from
the transmitter to the receiver. The signal may also be refracted by the troposphere. The
ground wave is composed of a direct wave, a ground reflected wave, a surface wave, and a tropospheric wave.
Figure 23 Possible routes for ground waves.
6. Direct Wave Component. The direct wave is that part of the ground wave that
travels directly from the transmitting antenna to the receiving antenna. The direct wave
is limited to line of sight distances. To increase the range, increase the height of either the transmitting or receiving antenna.
7. Ground Reflecting Component. The ground reflected component is that part of the
radio wave that is reflected before it reaches the receiving antenna. It may be reflected
from the ground or from a body of water. When the radio wave is reflected, the phase is
reversed. This could affect the reliability of communication. It could cancel out the radio
waves that travel directly to the receiving antenna. To minimize the canceling effect, the
antenna should be raised at either end.
8. Surface Wave Component.
a. The surface wave travels along the Earth's surface. It follows the curvature of the
earth. When both the receiving and transmitting antennas are located close to the earth, the direct and reflected wave may cancel each other out.
Table 3. Propagation Characteristics of Local Terrain
b. The surface wave is transmitted as a vertically polarized wave. When using the
surface wave, use a vertical antenna. A horizontal antenna transmits a horizontal wave
which is short circuited by the earth. The better the type of local terrain, the further the
17
signal will travel and not be absorbed. The range of the surface wave is determined by
how powerful the transmitter is. An increase in power will increase the surface wave
range. The range of the surface wave is also affected by the terrain features it must travel over.
9. Frequency Characteristics of Ground Waves.
a. The frequency used will determine which component of the ground wave will be
used. If the frequency is below 30 MHz the surface wave will be used primarily. Between
10 and 30 MHz the local terrain features will determine which component of the ground
wave will be used. At frequencies greater than 30 MHz the direct wave is primarily used
because the local terrain features absorb the surface and ground reflected waves. Above 30 MHz, vertical or horizontal polarization may be used.
b. Frequency bands use certain components of the ground wave:
(1) The low frequency band (30 to 300 kHz) is used for moderate distance ground
wave communication. A vertical antenna should be used in the low frequency band. The
radio wave follows the curvature of the earth for several hundred miles.
(2) The medium frequency band (300 kHz to 3 MHz) is used for moderate distance
communication over land and for long distance communication over sea water up to 1,000 miles.
(3) The high frequency band (3 to 30 MHz) is used for short distance communication.
At these frequencies, the local terrain absorbs more and more of the signal as the
frequency increases, decreasing the ground wave range. Long distance communications is possible using sky wave.
(4) The very high frequency band and higher bands (30 MHz and over) are used for
line of sight communication. Only the direct wave component of the ground wave is
usable. The range can be increased by raising the height of the antenna. Sky wave
communication is not possible because the frequencies pass through the ionosphere and are not reflected.
SKYWAVES.
1. Early radio communication was thought to be impossible over long distances. The
reasoning, local terrain would absorb the radio signal. When trans-atlantic
communication was accomplished, this opened up new questions. If the surface wave
was limited, then how did communication take place? The conclusion made was that the
earth was surrounded by something other than air. Two men, one an Englishman the
other an American, suggested that a electrified layer above the earth reflected radio signals. Later experiments showed that more than one layer existed.
2. Formation of the Ionosphere: As shown in figure 24 the earth's atmosphere extends
up to a distance of 250 miles. The level of ionization increases with height. The sun's rays combined with cosmic rays ionize these layers.
a. Ionization. The bombardment by the sun and ultraviolet rays charge the atoms in these layers. This action is called ionization.
b. Recombination. As the sun goes down and the intensity of the ultraviolet rays
decreases, the ionization of the layers decreases. Just before sunrise, ionization is at its
lowest point.
c. Source of ionization - the sun. The earth and the sun are composed of the same basic
elements. The violent state of these elements on the sun keeps it in a constant of state of molten or gaseous condition.
There is only one principal ionized layer at night.
18
Figure 24
Figure 25 Layers of the ionosphere.
a. D Layer. The D layer is approximately 30 to 55 miles above the earth. This layer has
the least ionization and therefore has the lease effect on radio frequencies. It is present
during the day only. The height varies over the eleven year sunspot cycle. The D layer is
approximately 6 miles thick. Present only during day time.
b. E Layer. The E layer is approximately 55 to 90 miles above the earth. The E layer
reflects radio frequencies up to about 20 MHz. The maximum one hop range of the E
layer is 1,500 miles. This layer is present only during the day. The height of the layer
varies during the eleven year sunspot cycle. The E layer is approximately 15 miles thick.
c. F Layer. The F layer is from 90 to 240 miles above the earth. The F layer is present
only at night. This layer is created when the F1 and F2 merge. Because it is the most
ionized, recombination takes place more slowly. The height varies over the course of the
eleven year sunspot cycle.
d. F1 and F2 Layers. During the daylight hours, the F1 layer has a height of
approximately 90 miles and is approximately 12 miles thick. The F2 layer has a height of
approximately 160 to 220 miles and is approximately 15 miles thick. The F2 layer, being
the closest to the sun, has the most ionization. The height of both layers varies over the
eleven year cycle of sunspot activity.
e. Other layers. Other layers or clouds appear from time to time over the eleven year
sunspot cycle. These layers appear near the E layer. Together, they are called the
Sporadic E layer.
19
Figure 26 Effect of frequency on the critical angle.
Figure 27 Relationship between skip zone, skip distance, and ground wave.
Basic types of Antenna
1. Hertz
o ½ wavelength long or any even or odd multiple thereof
o May be mounted either vertically or horizontally
o Need not be connected conductively to ground
2. Marconi
o ¼ wavelength or any odd multiple thereof
o mounted vertically and grounded
Figure 28 Types of Antenna
20
PROCEDURES AND REQUIREMENTS FOR NEW AM/FM/TV BROADCAST STATIONS
I. Congressional Franchise
II. File petition for certificate of public convenience (CPC) with the NTC
Category A: Corporation
1. Articles of Incorporation and By – Laws duly approved by the Securities and
Exchange Commission
2. List of present Officers and Board of Directors and the corporate secretary’s
Affidavit attesting to its present corporate structures
3. Duly accomplished information sheet of each and every member of the board
of Directors
4. Audited financial statement of the corporation for the last three (3) years and
copy of income tax returns for the same year
5. Economic viability study (for commercial stations) source of funds (for non-
commercial stations)
6. Technical feasibility study (signed and sealed by an Electronics and
Communications Engineer duly registered with the Philippine Regulatory
Commission).
7. Duly accomplished application for
a. Permit to Purchase Transmitter
b. Construction Permit
III. Public hearing shall be conducted
IV. The commission shall render decision on the petition
KBP PROGRAM STANDARDS (RADIO CODE OF THE KBP)
A. News • Each station is required to schedule a minimum of 45 minutes of news per day
(from 5am – 10pm) on a Monday thru Saturday basis
B. Public Affairs, Public Issues and Commentaries • Public affairs programs shall strive to contribute to national development and shall
aim at articulating as broad spectrum of opinions as possible.
C. Community Responsibility • Broadcasters shall acquaint themselves with the culture, mores traditions, needs
and other characteristics of the locality and its people to best serve the
community
D. Political Broadcasts • Political broadcast such as straight commentaries, analyses, reportage or in
drama form, designed to influence voters, shall be properly identified before and
after the program as paid broadcast.
E. Support to development and Nationalism • All station shall contribute to national development and shall promote the
education , cultural, social, economic up liftment of the people
F. Personal Calls and Appeals • Personal appeals or “panawagan” shall be carefully pre-screened by competent
station personnel to determine the legitimacy of such call. Person making the on-
air calls shall be briefed by the announcer or any competent station
representative on the proper broadcast decorum before they are allowed to go on-
air.
G. Public Complaints • Complaints by individuals or legitimate groups may be allowed only on issue
which affect the public welfare
H. Sex and Violence • The use of words and phrases which have undesirable and / or offensive
implications shall not be allowed. The use of undesirable, offensive, obscene,
blasphemous, profane or vulgar words and phrases shall not be allowed.
21
I. Drama Programming • A drama program shall strive to be innovative and shall reflect a degree of
creativity
J. Children’s Program • In their totality, children’s programs shall contribute to the sound, balanced
development and growth of children, thereby helping them achieve a sense of
awareness of the world around them
COMMERCIAL LOAD
A. In Metro Manila: • Commercial load for radio shall not exceed fifteen (15) minutes for one hour
program
• A haft hour program shall have a maximum of 7 ½ commercial minutes and a
quarter – hour program shall not exceed three (3) minutes and thirty seconds
• A five minute program shall have a maximum load of one (1) minute and fifteen
(15) seconds
B. Outside Metro Manila • Commercial load for radio shall not exceed seventeen (17) minutes for a one –
hour program outside Metro Manila.
• A haft hour program shall have a maximum of 8 ½ commercial minutes and a
quarter – hour program shall not exceed four (4) minutes.
• A five minute program shall have a maximum load of one (1) minute and thirty
(30) seconds shall be included in the computation of the maximum commercial
load allowed per clock hour.
ALLOCATION OF FREQUENCIES FOR AM BROADCAST STATION
a. 550 -1600Khz
b. 9 Khz separation for every station in the Philippines
c. Interference between stations is imminent if the minimum required distance is
greater than the aerial distance between stations.
Aerial distance – proposed distance – co channel distance = positive value
d. the required distance for co-channel station is 487, for the first (9Khz) adjacency
is 62 km. and for the second (18 Khz) adjacent is 3137 Km.
ALLOCATION OF FREQUENCIES FOR FM BROADCAST STATION
a. 88 – 108 Mhz (there are 100 assignments in this band and starts from 88.1 –
107.9 Mhz)
b. 200 Khz separation for every station
c. Classes of station (FM)
Class A: a station with an authorized transmitter power of not
exceeding 25 Kilowatt (Kw)
Class B: a station with an authorized transmitter power of not
exceeding 10 Kilowatt (Kw)
Class C: transmitter power not exceeding 1 kilo watt (Kw)
Class D: transmitter power not exceeding 10 Watts (W)
d. Intermediate Frequency (IF) amplifiers of most FM broadcast receivers are
designed to operate on 10.7 Mhz. For this reason the assignment of 2 stations In
the same area, one with a frequency of 10.6 or 10.08, removed from that of the
other, should be avoided if possible
e. Stations normally will not be authorized to operate in the same city or nearby
cities with a frequency separation of less than 8000 khz .
ALLOCATION OF FREQUENCIES FOR TV BROADCAST STATION
a. VHF Channels (CH: 1- 13); Range: 54 – 216 Mhz.
b. UHF Channels (CH: 14- 83); Range: 470 – 890 Mhz.
c. The bandwidth of TV broadcast channels shall be 6 Mhz
d. The visual carrier frequency shall be 1.25 Mhz. above the lower frequency limit of
the channel.
e. The unmodulated aural carrier frequency shall be 4.5 Mhz above the visual carrier
or 0.25 Mhz below the upper frequency limit of the channel
f. The visual carrier shall be amplitude modulated by the video signal.
22
TECHNICAL STANDARDS AND OPERATING REQUIREMENTS FOR AM BROADCAST
STATIONS IN THE PHILIPPINES
1. INTRODUCTION
Ever since the advent of radio, there have been progressive efforts in regulating
or controlling this medium of communication - primarily to minimize mutual interference
among growing number of stations. The use of radio in mass communications, or
broadcasting, eventually compelled governments, took the avoided task of formulating
rules, regulations and technical standards which are mostly so designed for the benefit of
the listening public.
In the formulation of Technical Standards for domestic broadcasting, the more
important considerations must include:
1. The prevention of harmful signal interference;
2. The provision for better signal quality, so that the listener may enjoy a
cleaner and more realistic sound reproduction;
3. The provision for technical facilities required for the production of
varied program formats that will satisfy the various listener's taste, and
4. The conservation of the broadcast spectrum
But better technical facilities mean huge outlays for the purchase of expensive
electronic gear. And, in the Philippines, where broadcasting is a free enterprise, the
degree of improvisation in technical facilities must be commensurate to the economic
capabilities of broadcast entities. The Kapisanan ng mga Broadkaster sa Pilipinas (KBP)
and the National Telecommunications Commission, cognizant of the criteria, have
designated professionals directly involved with the broadcast industry and
representatives of the government to revise existing local standards, or formulate new
standards, which shall be applicable to the country's industry and to the trends of the
time.
2. DEFINITION OF TERMS
2.1 Medium Frequency Broadcast Station
In as AM Broadcast Station licensed for aural or sound transmission intended for
direct reception by the general public and operated on a channel in the Medium
Frequency Band 535-1605 kHz.
2.2 Medium Frequency Broadcast Band
Means the band of frequencies extending from 535 to 1605 kHz
2.3 Medium Frequency Broadcast Channel
The band of frequencies occupied by the carrier and two (2) sidebands of an AM-
Broadcast Signal with the carrier frequency at the center. Channels shall be
designated by their assigned carrier frequencies starting from 531KHz in increments
of 10KHz.
2.4 Secondary Station
A station operating on any one channel and is designated to render service over a
primary service area which is limited by the subject to such interference as may be
received from a clear -channel station.
2.5 Carrier Wave
A sinusoidal voltage or current generated in a transmitter and subsequently
modulated by a modulating wave.
2.6 Carrier Frequency
Means the frequency of the carrier wave.
2.7 Operating Frequency
Means the carrier frequency at any particular time.
2.8 Authorized Frequency
The carrier frequency authorized by the National Telecommunications Commission.
2.9 Hertz
The term "Hertz" abbreviated "Hz", is used as a unit of frequency, supplanting the
term" cycle per second ".
2.10 Percentage Modulation (Amplitude)
"Percentage modulation" with respect to an amplitude modulation wave means the
ratio of the amplitude wave to the average amplitude expressed in percentage.
23
2.11 Maximum Percentage of Modulation
"Maximum percentage of modulation" means percentage of modulation that may be
obtained by a transmitter without producing in its output harmonics if the modulating
frequency in excess of those permitted by these regulations.
2.12 High Level Modulation
"High level modulation" is modulation produced in the last radio stage of the system.
2.13 Low Level Modulation
"Low Level Modulation" is modulation produced in an earlier stage than the final.
2.14 Plate Modulation
"Plate Modulation" is modulation produced by the introduction of the modulating wave
into the plate circuit of any of the amplifier stage in which the carrier frequency wave
is present.
2.15 Grid Modulation
"Grid Modulation" is modulation produced by the introduction of the modulating wave
into any of the grid circuits of any RF amplifier sage in which the carrier frequency
wave is present.
2.16 Operating Power
"Operating Power" is the power that is actually supplied to the radio station antenna.
2.17 Maximum Rated Carrier Power
"Maximum rated power" is the maximum power at which the transmitter can be
operated satisfactorily and is determined by the design of the transmitter.
2.18 Input Power
"Input power" is the product of the voltage and current at the output of the last radio
stage, measured without modulations.
2.18 Antenna Input Power
"Antenna input power" is the product of the square of the antenna current and the
antenna resistance at the point where the current is measured.
2.19 Antenna Current
"Antenna Current" is the radio frequency current in the antenna with no modulation.
2.20 Antenna Resistance
"Antenna Resistance" means the total resistance of the transmitting antenna system
at the operating frequency and at the point at which the antenna current is
measured.
2.21 Figure of Merit
"Figure of Merit" of a medium frequency serial system means the root-mean-square
(RMS) value of the unattenuated field strength (in milli volt per meter) at a distance
of 1.6 km from the serial in all directions in the horizontal plane divided by the square
root of the serial input power (in kilowatts).
2.22 Modulator Stage
"Modulator Stage" means the last amplifier stage off the modulating wave, which
modulates a radio- frequency stage.
2.23 Modulated Stage
"Modulated Stage" means the radio-frequency stage to which the modulator is
coupled and in which the continuous wave (carrier wave) is modulated in accordance
with the system of modulation and the characteristics of the modulating wave.
2.24 Last Radio Stage
"Last radio stage" means the oscillator of the radio frequency amplifier stage, which
supplies power to the antenna.
2.26 Daytime
The term "daytime" refers to that period of time between 2100 GMT to 1000 GMT
(5:00 AM -6:00 PM local standard time).
2.27 Nighttime
The term "nighttime" refers to that period of time between 1000 GMT to 2100 GMT
(6:00 - 5:00 AM local time).
2.28 Experimental Period
The term "experimental period" means that time between midnight to 5:00 AM local
standard time (1600-2100GMT). This period may be used for experimental purpose in
testing and maintaining apparatus by the licenses of any medium frequency
broadcast station on its assigned frequency and with its authorized power, provided
no interference is caused to other stations maintaining a regular operating schedule
within such period.
24
2.29 Field Strength
Means the root -mean-square value of the voltage-stress produced in space by the
electric field of a radio wave, and is expressed in volts per meter or in decibels (dB)
relative to it.
2.30 Effective Field
The term "effective" or "effective field intensity " is the root-mean-square (RMS)
value of the inverse distance field at 1.6 km from the antenna in all directions in the
horizontal plane.
2.31 Service Area
2.31.1 The term "primary service area" of a broadcast station means the area in which
the ground wave field of 3.16 MV/m (70dBu) is not subject to objectionable
interference of objectionable fading.
2.31.2 The term "secondary service are" of a broadcast station means the area served by
the sky wave and not subject to objectionable interference. The signal is subject
to intermittent variations in intensity.
2.31.3 The term "intermittent service area" of a broadcast station means the area
receiving service from the ground wave but beyond the primary service area and
subject to some interference and fading.
2.32 Audio-frequency (AF) Signal-to-Interference Ratio
Is the ration (expressed in dB) between the values of the voltages of the wanted
signal and the voltage of the interference, measured under specified conditions, at
the audio-frequency output of the receiver (CCIR Recommendation 447-1)
2.33 Audio-Frequency (AF) Protection Ratio
Is the agreed minimum value of the audio-frequency signal-to-interference ration
considered necessary to achieved subjectively defined reception quality. (CCIR
Recommendation 447-1)
2.34 Radio-Frequency (RF) wanted-to-interference Signal ratio
Is the ratio (expressed in dB), between the values of the radio-frequency voltage of
the wanted signal and the interference signal, measured at the input of the receiver
under specified conditions. (CCIR Recommendation 447-1)
2.35 Radio-Frequency (RF) Protection Ratio
Is the value of the radio-frequency wanted-to-interference signal ratio that enables,
under specified conditions, the audio-frequency protection ratio to be obtained at the
output of a receiver. (CCIR Recommendation 447-1)
2.36 Attended Transmitter
Attended transmitter means a transmitter where a qualified technician is in
attendance during all periods of its operation.
2.37 Potable Transmitter
The term "Potable Transmitter" means a transmitter constructed that it may be
moved about conveniently from place to place, and is in fact so moved about from
time to time, but not ordinarily use while in motion. In the medium frequency
broadcast band, such a transmitter is used in making field intensity measurement for
locating a transmitter site for a medium frequency broadcast station. A potable
broadcast station will not be licensed in the medium frequency broadcast band for
regular transmission of programs intended to be received by the public.
2.38 Carrier Shift
Means the variation of the mean carrier amplitude resulting from the process of
amplitude modulation; carrier shift is expressed in terms of variation produced at a
given percentage modulation by a sinusoidal test signal, the variation being
expressed as a percentage of the modulated carrier amplitude.
2.39 Combined Audio Harmonic
The term "combined audio harmonics" means the arithmetical sum of the amplitude
of all the separate harmonic components, root-sum-square (RSS) harmonic readings
maybe accepted under conditions prescribed by NTC.
2.40 Total Harmonic Distortion
Means the effective value of the harmonic voltages present in the audio frequency
output of the equipment under test. It is expressed as a percentage of the effective
value of the fundamental audio frequency voltage and the harmonic voltage present
in the output.
2.41 Noise Level
2.41.1 "Noise Level" means the root-mean-square (RMS) value of the voltage of spurious
origin present in the audio frequency output of the equipment under test,
expressed in decibels relative to a specified root-mean-square (RMS) value of
sinusoidal audio frequency voltage.
25
2.41.2 "Unweighted noise level" in a specified band means the noise level in that band
measured by an instrument, the frequency response in which is uniform over that
band.
2.42 Frequency Response
Means the variation, over a specified audio frequency range of the transmission
efficiency of the equipment under test; the variation is expressed in decibels relative
to the transmission efficiency at a specific frequency such as 1000 Hz.
2.43 Gain of an Audio Frequency Amplifier
Gain of an audio frequency amplifier of a chain of audio frequency equipment
incorporating one or more such amplifier means the ratio, expressed in decibels, of
the power delivered to the load at a specific frequency usually 1000Hz ton the power
which would be delivered to the same load if the amplifier or chain of equipment
where replaced by an ideal transformer matching the nominal load and source
impedances.
2.44 Spurious Emission
The emission of any frequency outside of the assigned channel or authorized band of
frequency and tolerances allowed by these regulations. Emissions outside of the
assigned channel as a result of the modulation process, is not considered spurious
unless it is due to over modulation.
2.45 Authority
Means the National Telecommunications Commission.
2.46 Licensee
Means the holder of a license for a broadcasting station from the National
Telecommunications Commission.
2.47 Qualified Technician
A person, who is a holder of a radio operator's license or its equivalent, as required
by these regulations, issued by the NTC.
3. TECHNICAL REQUIREMENTS
3.1 General Technical Requirements
Equipment shall be constructed with due regard to mechanical soundness, neatness
of wiring and accessibility for maintenance. Adequate testing and monitoring points
shall be provided to permit the isolation and testing of individual equipment.
3.1.1 Adequacy of Components
All component parts shall be in accordance with good engineering practice. Where
appropriate specifications of NTC or in its absence, component parts shall comply
with CCIR standards.
3.1.2 Compliance with Electrical Wiring Rules
All equipment using electrical power shall comply with rules of the Philippine
Electronics Code and the Philippines Electrical Code.
3.1.3 Regulation of supply voltage
Adequate voltage regulations shall be provided, where necessary, to insure that
equipment performance is not changed by variations in supply voltage
3.1.4 Protection
3.1.4.1 Protection persons
Having, regard for the high voltage employed in transmitting apparatus, adequate
provisions shall be made in the construction of all equipment and protective
enclosure, warning signs and safety switches shall be provided, in accordance with
good engineering practice, to ensure as far as practicable, the safety of all
persons.
3.1.4.2 It shall be the responsibility of the management or the licensee operating a
broadcasting station to ensure that protective devices are installed and
appropriate safety rules are observed.
3.1.4.3 Protection of equipment
Equipment shall be protected in accordance with good engineering practice,
against unsafe conditions and damage that may otherwise result under faulty
conditions.
3.2 Detailed Technical Requirements
3.2.1 Consideration of the Antenna System
The chief purpose of the medium wave radio broadcasting antenna is to
radiate efficiently the energy supplied by the transmitter, more so towards the
horizon or along the ground and least towards the sky. It is usually the vertical
tower radiators that meet these requirements successful over most other models
26
because of its superior ground wave propagation characteristics and simplicity of
antenna design.
The antenna, being the take-off point of radio waves, is the last element of the
system under the control of the radio broadcasting station. Radio waves radiated
from the transmitting antenna are propagated through space to the receiving
antenna. The only control over these propagated waves is in the selection of the
antenna site, the polarization, and the strength of the signal leaving the
transmitting antenna. Further consideration must be given directional antenna
system, which concentrates the amount of radiation in the direction(s) where it is
wanted and restricts the radiation in direction(s) where it is not wanted.
3.2.1.1 Location of Antenna Site
3.2.1.1.1 The main consideration in the selection of an antenna site are :
a. Location in relation to the population to be served and to other installation
and airports.
b. Conductivity of the soil at and immediately adjacent to the site;
c. Conductivity of the path between the site and the target area.
Before the approval of the NTC is given for any site, the matters will be
referred to the Bureau of Air Transportation (BAT), restrictions maybe imposed on
the height and location of masts in certain areas and obstruction painting and/or
lighting may be necessary. Except in the area now designated as antenna farm by
the BAT, masts or towers less than 150 feet from the ground in height may be
erected and are exempted from this provision. Masts or towers with heights above
150 feet from the ground are normally required to put up the standard obstruction
lighting and/or painting.
3.2.1.2 Antenna Design
3.2.1.2.1 The transmitting antenna system shall be vertically polarized and shall
radiate an effective field of not less than that of a 60-degree vertical radiator.
3.2.1.2.2 For economic reason, a single vertical tower radiator as mentioned above
maybe employed to serve as a common antenna (multiple frequency antennas)
for two or more stations provided the specifications of section 3.2.2.2.13 through
3.2.2.2.16 of these standards are satisfied.
3.2.1.2.3 In the case of a directional antenna system, its composition shall be of the
same vertical tower radiators as mentioned above, arranged to conform to a
design configuration that would emit the desired radiation pattern.
3.2.1.2.4 The antenna, antenna led-in, and counterpoise (if used), shall be installed
so as not to present a hazard. The antenna maybe located close by or at a
distance from the transmitter building. A properly designed and terminated
transmission line should be used between the transmitter and the antenna when
located at a distance.
3.2.1.2.5 The antenna radio frequency current meters (both regular and remote for any
other radio frequency instrument which is necessary for the operator to read)
shall be so installed permanently as to be easily and accurately read without the
operator having to risk contact with circuits carrying high potential radio
frequency energy.
3.2.1.2.6 It is not necessary to protect the equipment in the antenna tuning house and
the base of the antenna with screens and interlocks, however the door to the
tuning house and antenna base must be fenced and locked at all times, to ensure
that no unauthorized persons will gain access thus providing maximum safety to
lives. Ungrounded fence or wires must be efficiently grounded either directly or
through static leaks. Lightning protection for the antenna system must be
installed.
3.2.2 Transmitting Equipment
The transmitting equipment and facilities shall be layed out in accordance with
good engineering practice thereby providing ease, comfort, and safety to
personnel.
3.2.2.1 Location and Layout
The building shall be of a design and type of construction suitable to the area in
which it is located and it shall comply with relevant building regulation.
3.2.2.1.1 Adequate space shall be provided in the building to facilitate access to all
equipment for operation and maintenance purposes. Adequate space for staff
facilities shall also be provided.
3.2.2.1.2 Adequate ventilation and, where necessary, air-conditioning shall be provided
to ensure satisfactory working conditions for staff and equipment.
3.2.2.1.3 Adequate lighting shall be provided in all equipment rooms to facilitate
operation and maintenance of the equipment.
27
3.2.2.2 Design, Construction &Safety to Life:
3.2.2.2.1 The transmitter must be capable of delivering its rated carrier power, with
the provision for varying the same to compensate for variations in line voltage
and other factors, which may affect the power output.
3.2.2.2.2 The transmitter must be capable of delivering and maintaining its carrier
power within the required limits of 10% whether to be at full power daytime
within the required power nighttime mode. The power shall be determined by the
direct method. I, e., the square of the unmodulated antenna current multiplied by
the antenna resistance at the same point, or in the case of a directional antenna
system, its common input point resistance times its common input point current
squared. (The indirect method (Ep x Ip x efficiency of the last radio frequency
stage) may also be used.)
3.2.2.2.3 The transmitter must be capable of satisfactory Operation at the authorized
operating power with modulation of at least 85% with no more distortion than
given below.
3.2.2.2.4 The transmitter must be capable of maintaining the operating frequency within
the limits of + 10 hertz of the assigned frequency.
3.2.2.2.5 The Carrier shift (current) at any percentage of modulation shall not
exceed 5%.
3.2.2.2.6 The Carrier hum and extraneous noise level, unweighted R.S.S. (exclusive
of the microphone and studio noises) over the frequency band 30 to 20000 hertz
is at least 45 dB below the level of a sinusoidal tone of a 400 Hz, producing 100%
modulation of the carrier.
3.2.2.2.7 The total Audio frequency distortion from (microphone terminals, including
microphone amplifier, to antenna output must not exceed 5% harmonics voltage
measurement of arithmetical sum or R.S.S) when modulated from 0 to 84%, and
not over 7.5% harmonics when modulating from 85% to 95%. Distortion shall be
measure with modulating frequencies of 50,100,400,1000 and 5000 hertz up to
the tenth harmonics or any intermediate frequency that reading on these
frequencies indicate is desirable.
3.2.2.2.8 The Audio frequency transmitting characteristics of the equipment form the
microphone terminal (including microphone amplifier unless microphone
frequency connection is included, in which event proper allowance shall be made
accordingly) to the antenna output does not depart more than 2 dB from that at
1000 cycles between 100 and 5000 hertz
3.2.2.2.9 The transmitter must be equipped with suitable and properly working
indicating instruments to continuously measure the LC plate current and voltage
and any other indicating instruments necessary for proper operation.
3.2.2.2.10 The transmitter shall be equipped with an adequate control system for the
application and removal of power
3.2.2.2.11 Adequate margin shall be provided for all component parts to avoid over
heating at the maximum rated power output.
3.2.2.2.12 Any emission appearing on a frequency removed from the carrier by between
15kHz and 30 kHz inclusive shall be attenuated at least 25dB below the level of
the unmodulated carrier.
3.2.2.2.13 Any emission appearing on a frequency removed from the carrier by more
than 30kHz and up to top and including 75kHz, inclusive, shall be attenuated at
least 35dB below the level of the unmodulated carrier.
3.2.2.2.14 Any emission appearing on a frequency removed from the carrier by more
than 75kHz shall be attenuated at least 43+10 log (power in watts) decibels or 8
whichever is lesser.
3.2.2.2.15 The transmitter shall be operated, tuned, and adjusted, so that the emission
outside of the authorized channel do not cause harmful interference to the
reception to the reception of other stations. In any case, should harmful
interference to the reception of other radio stations occur, the licensee may be
required to take further step as may be necessary to eliminate the interference.
3.2.2.2.16 In general, the transmitter shall be constructed either on racks and panels or
in totally enclosed frames protected as required by the Philippine Electronics Code
and the Philippine Electrical Code. The final stages of high power transmitters
may, however, be assembled in open frames provided that such stages are
enclosed by a protective fence.
28
3.2.2.2.17 Means shall be provided for making all tuning adjustments of any circuit
involving the application of voltages in excess of 350 Volts from the front panel
with all access doors closed.
3.2.2.2.18 Bleeder resistance or such other automatic means shall be installed across all
the condenser banks to remove any change, which may remain after the high
voltage circuit is opened.
3.2.2.2.19 Plate supply and other high voltage devices, including transformers, filter,
rectifiers, and motor generator, shall be provided with protective circuits so as to
prevent injury to operating personnel.
3.2.2.2.20 Commutator guards shall be provided in all high voltage rotating machinery.
Coupling guards on motor generators are optional.
3.2.2.2.21 In case the voltmeter is located on low potential side of the multiplier resistor
with one terminal of the instrument at or less than 1000 volts above ground, no
protective case is required. However, it is a good practice to protect voltmeters
that are subject to more than 5000 volts with suitable over voltage protective
device across the instrument terminal in case the windings open.
3.2.2.2.22 Wiring between units of the transmitter, with the exception of circuits carrying
radio frequency energy, shall be installed in conduits or approved fiber or metal
raceways to protect it from mechanical injury.
3.2.2.2.23 Circuits carrying low level radio frequency energy between units of the
transmitter shall be properly wired and shielded to prevent the pick up of
modulated radio frequency energy from the output circuits.
3.2.2.2.24 Each stage (including the oscillator) preceded the modulated stage shall be
properly shielded and filtered to prevent feedback from any circuit following the
modulated stage.
3.2.2.2.25 A type approved modulation monitor which either be an oscilloscope or a
meter indicator type is required to be installed and operated continuously where
there is a transmitter. However, in the case of a consolidated operation, whereby
two (2) or more transmitters are co-located and housed under one roof,
maintaining one modulation monitor for the purpose will suffice.
3.2.3 Metering Equipment
3.2.3.1 Linear scale instrument indicating the plate voltage of the last radio stage
shall meet the following specifications:
1. Length of scale shall not be less than 6 cm.
2. Accuracy shall be at least 2 % of the full reading.
3. The maximum rating of the meter shall be such that it does not read off scale
during modulation.
4. Full-scale reading shall not be greater than five times the minimum normal
indication.
3.2.3.1.1 Instrument indicating antenna current, common point current, and base
currents shall meet the following specifications:
Instrument having logarithmic or square law scale:
a. Shall meet the requirement of paragraph 3.2.3.1 (1), (2), and (3) of this
section for linear scale instruments.
b. Full-scale reading shall not be greater than three times the minimum normal
indicator.
c. No scale division above one-fifth-scale reading (in amperes) shall be greater
than one-fiftieth of the full-scale reading. (Ex. An ammeter meeting requirement
(1) is acceptable for indicating currents from 1 to 5 amperes, provided no division
between 1 and 5 amperes is greater than one-fiftieth of 5 amperes, 0.1 amperes.)
d. Manufacturer's data of instrument of the expanded scale type must be
submitted to the NTC showing that instruments have acceptable expanded scales.
Furthermore, the type number of these instruments must include suitable
designations.
3.2.3.1.2 A radio frequency ammeter meeting the requirements of paragraph (b) of this
section shall be permanently installed in the antenna circuit or a suitable jack and
plug arrangement maybe made to permit removal of the meter from the antenna
circuit so as to protect it from damage by lightning. Where jack and plug
arrangement is used, contacts shall be protected against corrosion. Insertion and
removal of the meter shall not interrupt the transmission of the station. When
remove from the antenna circuit, the meter shall be stored in a suitable housing
at the base of the tower in which it is used. Care shall be exercised in handling the
meter to prevent damage that will impair its accuracy. Where the meter is
permanently connected in the antenna circuit, provision may be made to short or
29
open the meter circuit when it is not being used to measure antenna current.
Such switching shall be accomplished without interrupting the transmission.
3.2.3.1.3 Remote reading antenna ammeter (s) may be employed and the indications
logged as the antenna current, or in the case of a directional antenna, the
common point current and base current, in accordance with the following:
3.2.3.1.3.1 Remote reading antenna common point or base ammeters may be
provided by:
a. Inserting a second thermocouple or other device directly in the antenna circuit
with the remote leads to the indicating instrument.
b. Inductive coupling to thermocouple or other device for providing direct current
to indicating instrument.
c. Capacity coupling to thermocouple or other device for providing direct current
to indicating instrument.
d. Current transformer connected to second thermocouple or other device for
providing direct current to indicating instruments.
e. Using transmission line current meter at transmitter as remote reading
ammeter.
f. Using indication of phase monitor for determining the antenna base currents
or their ratio in the case of directional antennas, provided that the base
current readings are logged in accordance with the provision of the station
license, and provided further that the indicating instruments in the are
connected directly in the current sampling circuit with no other shunt circuits
of any nature. The meters in the phase monitor may utilize arbitrary scale
divisions provided a calibration curve showing the relationship between the
arbitrary scale and the scale of the base maters is maintained the transmitter
location.
g. Using indications of remote control instruments, provided that such indicating
instruments are capable of being connected directly into the antenna circuit at
the same point as the antenna ammeter.
3.2.3.1.3.2 Remote ammeters shall be connected into the antenna circuit at the same
point, as, but below (transmitter side), the antenna ammeter (s), and shall
be calibrated to indicate within to 2% of the regular meter over the entire
range above one-third or one-fifth full scale.
3.2.3.1.3.3 The regular antenna ammeter, common point ammeter, or base current
ammeter shall be above (antenna side) the coupling to the remote meters
on the antenna circuit so they do not read the current to the ground
through the remote meter (s).
3.2.3.1.3.4 Al remote meters shall meet the same requirement as the regular antenna
ammeter with respect to scale accuracy, etc.
3.2.3.1.3.5 Calibration shall be checked against the regular meter at least once a
week.
3.2.3.1.3.6 All remote meters shall be provided with shielding or filters necessary to
prevent any feedback from the antenna to the transmitter.
3.2.3.1.3.7 In the case of shunt of exited antenna, the transmission line current meter
at the transmitter may be considered as the remote antenna ammeter
provided the transmission line is terminated directly into the excitation
circuit feed line, which shall employ series tuning only (no shunt circuit of
any type shall be employed) and, in as much as is practicable, the type
and scale of the transmission line meter shall be the same as those of the
excitation circuit feed line meter (meter in slant wire feed line or its
equivalent).
3.2.3.1.3.8 Remote reading antenna ammeters employing vacuum tube rectifiers or
semiconductor devices are acceptable, provided:
a. The indicating instrument shall meet all the above requirements for linear
scale instruments.
b. Data are submitted under oath showing that the unit has an overall
accuracy
of at least 2 percent of the full-scale reading.
c. The installation, calibration, and checking are in accordance with the
requirements of this paragraph.
3.2.3.1.3.9 In the event that there is any question as to the method of providing the
remote indication or the accuracy of the remote meter, the burden of proof
of satisfactory performance shall be upon the licensee and the
manufacturer of the equipment.
30
3.2.3.1.4 Since it is usually impractical to measure the actual antenna current of a
shunt excited antenna system, the current measured at the input of the
excitation circuit feed line is accepted as the antenna current.
3.2.3.1.5 The function of each instrument shall be clearly and permanently shown on
the instrument itself or on the panel immediately adjacent thereto.
3.2.3.1.6 Digital meters, printers, or other numerical load-out devices may be used
in addition to or in lieu of indicating instruments meeting the specification
of paragraph (a) and (b) of this section. If a single digital device is used at
the transmitter for reading and logging of operating parameters, either (1)
indicating instruments meeting the above-mentioned specifications shall be
installed in the transmitter and antenna circuit, or (2) a spare digital device
shall be maintained at the transmitter with the provision for its rapid
substitution for the main device, should that device malfunctions. The
read-out of the device shall include at least three digits and shall indicate
the value or a decimal multiple of the value of the parameter being read to
an accuracy of at least 2 percent. The multiplier to be applied to the
reading of each parameter shall be indicated at the operating position of a
switch used to select the parameter for display, or on the face of an
automatically printed log at least once calendar day.
3.2.3.1.7 The antenna ammeter (both regular and remote) and any other radio
frequency instruments which is necessary for the operator to read without
the operator having to risk contact with circuits carrying high potential
radio frequency energy.
3.2.3.1.8 Frequency Monitor Specifications:
a. The unit shall have an accuracy of at least 5% parts per million under
ordinary conditions of temperature and humidity encountered in standard
broadcast stations throughout the Philippines.
b. The range of the indicating device shall be at least from 20 hertz below to
20 Hertz above the assigned frequency.
c. The scale of the indicating device shall be so calibrated as to be accurately
road within at least 1Hertz.
3.2.4 Studio, Equipment, & Allied Facilities
The studio, being the source of programs must be provided with such control
room, equipment and other accommodation as are necessary to ensure the
provision of a satisfactory service by station.
3.2.4.1 Studio location and Layout
3.2.4.1.1 The building that will contain the studio shall satisfy the provision
given in sections 3.2.2.1.1 through 3.2.2.1.3 of these standards.
3.2.4.1.2 Each studio shall be associated with a control room from which the
operational area of the studio maybe viewed with ease. The NTC may,
however approve an operation whereby the studio and control rooms are
integrated into one and that responsible personnel shall perform simple
front panel type functions like level adjustments and switching during
his/her board hours, provided, a licensed radio technician with a 1st, 2nd, or
3rd, class radio telephone license is employed to perform all the more
complicated pre and post sign-on adjustments of a more technical nature
including maintenance jobs which are necessary for the proper operation of
the technical studio equipment. Provided further, that for this kind of
operation, an automatic program level control is employed to insure that a
proper program level is fed to the transmitter.
3.2.4.1.3 Studios and control rooms shall be so constructed that they are
adequately insulated from sources of extraneous noises and vibration, and
the acoustic treatment of such studios and control rooms shall be in
accordance with good engineering practice.
3.2.4.1.4 The following basic equipment shall be maintained in the station's
studio:
a. Two (2)-Microphones (one announce mike and one quest mike) of good
quality preferably with a unidirectional pattern, which shall pass a
relatively flat frequency response with in +2dB to audio impressions from
50 Hz to 10000 Hz when referred to1000 Hz from a source at a distance of
to 15 cm away.
b. Two (2) or three speeds type transcriptions turntable capable of
running within +0.3 rpm, to avoid objectionable wow and flutter. It shall
also run smoothly so that its associated pick-up and equalizer units may
not reproduce discernible extraneous noise and rumble when silent groove
31
record is played therein. The same pick-up and equalizer units shall pass a
relatively flat frequency response within +2dB to a frequency range from
50Hz to 10000Hz when referred to 1000Hz. The turntable shall have a 25
to 40 cms diameter platen
c. Two (2) - Tape Playback machines of either the reel type or the
cartridge/cassette type or one of each type, which shall run with +0.2% of
anyone of the standards average type speeds of 3 1/4 ips, 7 1/2 ips, and
15 ips, with a relatively flat frequency response within +2dB to a frequency
range of from 50Hz to 10000Hz when referred to 1000Hz.
d. One (1) - Audio Control Mixer with six (6) or more faders. Its
associated amplifiers shall pass a relatively flat frequency response to
within +2dB to an audio frequency range of from 50Hz to 10000Hz when
referred to 1000Hz.
e. Two (2) - Local Program and Cue Monitoring System with its associated
amplifiers and speakers that will pass a relatively flat frequency to within
+2dB to an audio frequency range of from 50Hz to 10000Hz when referred
to 1000Hz.
f. One (1) - Automatic Program Level Control amplifier that shall pass a
relatively flat frequency response to within +2dB to an audio frequency
range of from 50Hz to 10000Hz when referred to 1000Hz.
g. One (1) - Monitor Receiver.
h. One (1) - Tape Recording Machine of either the reel type or the
cartridge/cassette type or one of each type, which shall run within +0.2%
of anyone of the standard average tape speeds of 3 1/4 ips, 7 1/2 ips, and
15 ips, with a relatively flat frequency response within +2dB to an audio
frequency range of from 50Hz to 10000Hz when referred to 1000Hz.
3.2.5 Emergency Equipment and Facilities
Either an alternate main transmitter or an auxiliary transmitting
equipment, which ever is applied for the purpose by the user, in addition to
the main transmitter, may be authorized by the NTC provided a need
exists, such as a 24 - hour operating schedule or for alternate operation
during maintenance periods or where development work requires alternate
operations. Provided further, that the said transmitter meets the foregoing
standards herein already laid down along with the following provisions.
3.2.5.1 Alternate Main Transmitter
3.2.5.1.1 That both the regular and this alternate main transmitter be co-l
ocated in a single place.
3.2.5.1.2 That both transmitters (regular and alternate main) shall maintain
the same parameters especially with regard to authorized power,
frequency stability, audio frequency range, audio harmonic generation,
radio frequency harmonic and other spurious radiation.
3.2.5.2 Auxiliary Transmitter
3.2.5.2.1 Maybe installed either in the same location as the regular main
transmitter or in another location.
3.2.5.2.2 Its operating power maybe less but never greater than the
authorized power of the regular main transmitter.
3.2.5.2.3 A licensed operator shall be in control whenever an auxiliary
transmitter is placed in operation.
3.2.5.2.4 The auxiliary transmitter shall be maintained so that it may be
placed in operation at any time for one of the following purpose:
a. The transmission of the regular program upon the failure of the regular
main transmitter.
b. The transmission of the regular program during maintenance or
modification work (s) on the regular main transmitter necessitating
discontinuance of operation.
c. Upon request of a duly authorized representative of the NTC.
d. Shall be tested at least once a week either on-air (only between 12
midnight and 4 AM local standard time) or through a dummy load.
3.2.5.2.5 When installed in a location different from that of the regular main
transmitter, a type approved modulation monitor is required to be installed
along with it.
3.2.5.3 Emergency Electric Power Generating Unit
Depending on the prevailing circumstances, where the need exists, an
electric power generating unit with sufficient electrical capability to sustain
the station's emergency or regular operations may be maintained to insure
32
an uninterrupted operation. Should this generating unit, however, in the
course of its operation, cause or emit radio frequency energy and/or
harmonics that may prove harmful to the purity of the station's signal,
such interference shall be contained sufficiently as to satisfy the provisions
of sections 3.2.2.2.12 through 3.2.2.2.15 of these standards.
3.2.5.4 Emergency Announce Equipment Complement
Where the need exists an emergency announce equipment complement of
the types covered in section 3.2.4.1.4 parts a, b, c, d and e of these
standards shall be maintained in the transmitter side for emergencies, to
insure uninterrupted programming during the stations authorized hours of
on-air operations.
3.2.5.5 Spare Component Parts
In order to cut down-times during scheduled on-air operations, a
reasonable variety and number of spare components appropriate to the
equipment installed at the site, shall be kept on hand at each studio and
transmitter sites in most convenient location therein.
3.2.5.6 Fire Fighting Facilities
Appropriate and adequate fire fighting facilities shall be maintained within
the establishment, especially in fire prone areas therein.
3.2.6 Broadcast Transmission Services
Broadcast transmission service fall under these three categories:
1. Studio-to-transmitter link (STL)
2. Remote Pick-Up Broadcast Station
3. Communications, Coordination and control Link
The frequency bands authorized for the above service are as follows:
FREQUENCY BAND STUDIO-TOTRANSMITTER LINK
Band A 310-315MHz
Band B 734-752MHz
860-880MHz
942-952MHz
REMOTE PICK-UP BROADCAST STATION
Band A 305-310MHz
Band B 450-451MHz
Band C 455-456MHz
COMMUNICATIONS, COORDINATION AND CONTROL LINK
Band A 4-12MHz (non-exclusive)
Band B 26.10-2648MHz
Band C 162.235-162MHz
166.250 and 170.150MHz
Band D 880-890MHz
The NTC shall authorize the employment of any of these broadcast transmission
services to a station depending on the necessity and availability of frequencies for the
purpose. Any AM or FM station authorized to operate is entitled to use any broadcast
transmission services relevant to the efficient operation of the station where the use of
physical line or cables is not feasible.
3.2.7 Remote Control System
Operation of a transmitter by remote control may be authorized by the
NTC.
3.2.8 Directional Antenna System
The operation of a directional antenna system may be authorized by the
NTC on a non-interference basis.
4. OPERATING REQUIREMENTS
4.1 Hours of Operation
4.1.1 Minimum Operation Schedule-except Sundays and special holidays, the minimum
operating schedule of two-thirds of the total hours that it is authorized to operate
between 6AM and 6PM and midnight local standard time, except that in
emergencies when, due to causes beyond the control of the licensee. It becomes
impossible to continue operating, the station may cause operations for a period not
exceeding 10 days, provided that the NTC and its Engineer in-charge of the regional
33
district wherein the station is located, shall be notified in writing before the lapse of
the 10-day period after the emergency developed.
4.1.2 Broadcast(s) outside of the authorized regular operating schedules (as before
regular sign-on schedules and/or beyond the regular sign-off schedules) may be
aired without prior authorization from the NTC provided the program falls under an
emergency category or of very important relevance to the station's existence,
provided further, that not later than 10 days from the airing of such emergency
programs, a letter of notification is sent to the NTC and its District Engineer
responsible for the area, explaining the reasons for airing such broadcast(s), its
substance, time of airing duration, and such other pertinent information that may
be of value. The same information shall be entered in the program and operating
logs at the time the same was aired.
4.1.3 If a permanent discontinuance of operating is being contemplated, the licensee shall
notify in writing the NTC and its Engineer in-charge of the regional district where
the station is located at least two (2) days before the actual discontinuance is
affected.
4.1.4 Other Operating Practices
The percentage of modulation shall be maintained as high as possible consistent
with good quality transmission and in no case more than 125 percent on positive
peaks no more than 100 percent on negative peaks of frequent recurrence during
any selection which is transmitted at the highest level of the program under
consideration.
4.2 Posting of Station and Operator Licenses
4.2.1 The station license and other instrument of station authorization shall be posted in
conspicuous place in such a manner that all terms are visible, at the place the
licenses considers to be the principal control point of the transmitter. At all other
control points listed on the station authorization, a photocopy of the station
license and other instruments of station authorization shall be posted.
4.2.2 The original copy of the operator’s license shall be posted at the place where he is
on duty as an operator.
4.3 Operator Requirements
4.3.1 A radio operator holding a valid radio telephone first class operator’s license
except as provided in Section 4.4.2 shall be in actual charge of the transmitting
apparatus and shall be on duty either at the location or remote control point.
4.3.2 A station which is authorized for non-directional operation with a power of 10
kilowatt or less may be operated by persons holding a commercial radio operator’s
license of any class, except on aircraft radio-telephone operator ‘s authorization or
a temporary limited radiotelegraph second class operator’s license, when the
equipment is so designed that the stability of the frequency is maintained by the
transmitter itself within the limits f tolerance specified, and none of the
operations, except those specified in sub-paragraphs (1) through (4) of this
paragraph, necessary to be performed during the course of normal operation may
cause off-frequency operation or result in any unauthorized radiation.
Adjustments of transmitting equipment by such operators, except when under the
immediate supervision of a radiotelephone first class operator, shall be limited to
the following:
1. Those necessary to commence that may be required as a result of
routine matter.
2. Those external adjustments that may be required as a result of
variations of primary power supply.
3. Those external adjustments, which may be necessary to insure
modulation within the limits, required.
4. Those adjustments necessary to effect any change in operating power
that may be required by the station’s instrument of authorization.
Should the transmitting apparatus to observed to be operating in a
manner inconsistent with the station’s instrument of authorization and
none of the above adjustments are effective in bringing it into proper
operation, a person holding other than a radiotelephone first class
operator'’ license and not acting under the immediate supervision of a
radiotelephone first class operator, shall be required to terminate the
stations emissions.
4.3.3 The license of a station which is operated by one or more operator’s holding other
than a radiotelephone first class operator’s license shall have one or more
operators holding a radiotelephone first class operator’s license in regular full time
34
employment at the station whose primary duty shall be to effect and insure the
proper functioning of the transmitting equipment.
4.4 Station identification Announcement
4.5.1 A license of a medium frequency broadcast station shall make station
identification announcements (call letter, frequency, and location) at the
beginning and ending of each time of operation and during operation on the hour
and either on the half hour or at the quarter hour preceding the next hour:
provided,
4.5.2 Such identification announcement need not be made on the hour when to make
such announcement would interrupt a single consecutive speech, play, religious
services, symphony concert, or operatic production of longer duration than 30
minutes. In such cases, the identification announcement shall be made at the
beginning of the program, at the interruption of the entertainment continuity.
4.5.3 Such identification announcement need not to be made on the half hour or
quarter hour when to make such announcement would interrupt a single
consecutive speech, play, religious service, symphony concert. Or operatic
production. In such cases an identification announcement within five minutes or
either on the half-hour of identification announcements.
4.5.3 In the case of variety show programs, basketball game broadcasts, or similar
programs or longer duration than 30 minutes, the identification announcement
shall be made within 5 minutes of the time specified in section 4.5.1.
4.5.4 In the case of all other programs, the identification announcement shall be made
within 2 minutes of the times specified in section 4.5.1
4.6 Logs
The licenses or permitee of each medium frequency broadcast station shall
maintain program and operating logs shall require entries to be made as follows:
4.6.1 In the program Log:
4.6.1.1 An entry of time each station identification announcement (call letters,
frequency, and location) is made.
4.6.1.2 An entry briefly describing each program broadcast, such as “music”
“drama” “speech”, etc. together with the name or title thereof, and the sponsors
name, with the time of the beginning and ending of the complete program. If a
mechanical record is used the entry shall show the exact nature thereof, such as
“record”, “transcription”, etc., and the time it is announced as a mechanical
record. If a political candidate makes a speech, the name and political affiliations
of such speaker shall be entered.
4.6.1.3 An entry showing, for each sponsored program broadcast has been
announced as sponsor, paid for, or furnished by the sponsors.
4.6.1.4 An entry showing, for each program of network origin, the name of the
network originating the program.
4.6.2 In the Operating Log:
4.6.2.1 An entry of the time and station begins to supply power to the antenna and
the time it steps.
4.6.2.2 An entry of the time the program begins and ends.
4.6.2.3 An entry of each interruption of the carrier wave, its cause, and duration.
4.6.2.4 An entry of the following every 3o minutes.
a) Operating constants of the last radio frequency stage plate current and plate
voltage.
b) Antenna current.
4.6.2.5 Any other entries required by the instrument of authorization.
4.6.2.6 A log of all operation must be kept during the experimental period. If the
entries required above are not applicable thereto, then the entries shall be made
so as to fully describe the operation.
4.6.2.7 Logs of medium frequency broadcast stations shall be retained by the
licensed or permitee for a period of two (2) years: Provided, however, that logs
involving communications incident to a disaster or which include communications
incident to or involved in an investigation by the National Telecommunications
Commission and concerning which the license or permitee has been notified, shall
be retained by the licensee or permitee has been notified. Shall be retained by the
licensee or permitee until he is specifically authorized in writing by the National
Telecommunications Commission to destroy them: Provided, further, that logs
incident to or involved in any claim or complaint of which the licensee or permitee
has notice shall be retained by the licensee or permitee until such claim or
35
complaint has been barred by the statute limiting the time for filing of suits upon
such claims.
4.6.2.8 Each log shall be kept by the persons to dust, having actual knowledge of
the facts required, who shall sign the log when starting duty and again when
going off duty. The logs shall be made available upon request by an authorized
representative of the National telecommunications Commission
4.6.2.9 The log shall kept in an orderly manner, in suitable form, and in such detail
that the data required for the particular class of station concerned are readily
available. Key letters or abbreviations maybe used if proper meaning or
explanation is contained elsewhere in the log.
4.6.2.10 No log or portion thereof shall be erased, obliterated, or willfully destroyed
within the period of retention provided by the rules. Any necessary correction may
be made only by the originating the entry that shall strike out the erroneous
portion, initial the correction made, and indicate the date of correction.
4.6.2.11 Rough log may be transcribed into condensed form, but in such cases the
original rough log or memoranda and all portions thereof shall be preserved and
made a part of the complete log.
4.7 Remote Control Operation
Operation by remote control shall be subject to the following conditions
4.7.1 The equipment at the operating and transmitting positions shall be so installed
and protected that it is not successible to or capable of operation by persons other
than those duly authorized by the licensee.
4.7.2 The control circuits from the operating positions to the transmitter shall provide
positive on and
off control and shall be such that open circuits, short circuits, grounds or other
line faults will not actuate the transmitter and any fault causing loss of such
central will automatically place the transmitter in an inoperative position.
4.7.3 A malfunction of any part of the remote control equipment and associated line
circuits resulting in improper control or inaccurate meter readings shall be cause
for the immediate cessation of operation by remote control.
4.7.4 Control and monitoring equipment shall be installed so as to allow the licensed
operator at the remote control point to perform all the functions in a manner
required by the rules.
4.7.5 The indications at the remote control point of the antenna current meter for
directional antenna, The common point current and remote case current meters
shall be read and entered in the operating log each half-hour.
4.7.6 The indications at the transmitter, if a directional antenna station, of the common
point current, base currents, phase monitor sample loop currents, and phase
indications shall be read and entered in the operating log once each day for each
pattern. These readings must be made within two hours after the commencement
of operation for each pattern.
4.7.7 All stations, whether operating by remote control or direct control, shall be so
equipped as to be able to follow the prescribed EBS alerting procedures set for in
the EBS manual for Broadcast Stations.
4.7.8 Stations with authorized operating power in excess of 10 kilowatt employing
directional antenna and operated by remote control, shall make a skeleton proof
of performance each year, consisting of three or four measurement on each radial
used in the original application and must submit the results of these
measurements, plus the monitoring point readings with renewal application.
4.8 Maximum Power Allocation
Area MAXIMUM POWER IN KW
Low Band Mid Band High Band
525-918 KHz 919-1312 KHz 1313-1705 Khz
METRO MANILA
AND METRO CEBU 10 20 30
ALL OTHER AREAS 5 10 15
The maximum power stated above must conform to protection ratios
embodied the allocation rules and regulations for the medium wave band and
therefore shall be acted upon on a case to case basis.
36
4.8.1 Allocation Rules and Regulations
As derived from Annex 2 page 43 sections 4.4.1, 4.4.2, and 4.5 of the final
acts of the regional Administrative LF/MF Broadcasting Conference (Regions 1 and
3) Geneva, 1975 are the following allocation rules:
Frequency R.F. Signal Ratio R.F. Protection
(Ratio (dB)
Co-channel 73 dBU is to 43 dBU 30
(Same Frequency) (4.47 mV/m) (141.25 uV/m)
1st-Adjancency 73 dBU is to 64 dBU 9
(9-KHz away) (4.47 mV/m) (1.6 mV/m)
2nd-adjacency 97 dBU is to 73 dBu 24
(18-KHz away) (70.8 mV/m) (4.47 mV/m)
TECHNICAL STANDARDS AND OPERATING REQUIREMENTS FOR FM BROADCAST
STATIONS IN THE PHILIPPINES
1. INTRODUCTION The increasing importance of the role of FM broadcasting in the Philippine
has Encouraged broadcast engineers and the National Telecommunications
commission to pool their resources together and come up with the technical
standards and rules and regulations relating to FM broadcast.
These technical standards and regulations were derived from CCIR
recommendations, relevant engineering data, rules, and regulations of the Federal
Communications Commission, and other data supplied by manufacturers of radio
equipment and by licensee of FM broadcast stations. These standards and
regulations shall be revised from time to time to be effective and compatible with
technical progress.
2. FREQUENCY BAND The FM broadcast consist of that portion of the radio frequency spectrum from
88Mhz to 108 Mhz. The band is divided into 100 channels of 200 KHz, wide start from
88.1 MHz to 107.9 MHz.
3. DEFINITIONS 3.1 FM Broadcast Band means the band of frequencies extending from 88 to 108 Mega-
Hertz.
3.2 FM Broadcast channel means a band of frequencies 200 kilo Hertz in the Wide and is
designated by its center frequency. Channels for FM broadcast stations begin at 88.1
mega-Hertz and continue in successive steps of 200 kilo Hz to and including 107.9
mega Hertz.
3.3 FM Broadcast Station means a station employing frequency modulation in the FM
broadcast band and licensed primarily for the transmission of radiotelephone
emissions intended to be received by the general public.
3.4 Frequency Modulation means a system of modulation where the instantaneous
frequency varies in proportion to the instantaneous amplitude of modulating signal
(amplitude of modulating signal to be measured after pre-emphasis, if used and the
instantaneous radio frequency is independent of the frequency of the modulating
signal.
3.5 Center Frequency
3.5.1 The average frequency of the emitted wave modulated by sinusoidal signal.
3.5.2 The frequency of the emitted wave without modulation.
3.6 Frequency Swing means the instantaneous departure of the frequency of the Emitted
wave from the center frequency resulting from modulation.
3.7 Antenna Height Above Average Terrain
3.7.1 The height of the radiation center of the antenna above the terrain 3 to 16
kilometers from the antenna. (Generally, a different antenna height will be
determined for each radial direction from the antenna. The average of these
various heights is considered as the antenna height above average train).
37
3.7.2 Where circular or elliptical polarization is employed the antenna height above
average terrain shall be based upon the height of the radiation center of the
antenna which transmits horizontal components of radiation.
3.8 Antenna Field Gain of an FM broadcast means the ratio of the free space field
intensity produced at 1.6 kilometers in the horizontal plane expressed in millivolts per
meter for one (1) kilowatt antenna power to 137.6 millivolts per meter.
3.9 Antenna Power Gain means the square of the ratio of the root-mean-square free
space field strength produced at 1.6 kilometers in the horizontal plane, in millivolts
per meter. This ratio should be expressed in decibels (dB). (If specified for a
particular direction, antenna power gain is based on the field strength in that
direction only.)
3.10 Effective Radiated Power means the product of the transmitter power (transmitter
output power less transmission line loss) times (1) the antenna powers gain or (2)
the antenna field gain squared. Where the circular or elliptical polarization is
employed, the term “effective radiated power” is applied separately to the horizontal
and vertical components of the radiation.
3.11 Field Intensity as used in these standards hall mean the electric field intensity in
the horizontal direction.
3.12 Free Space Field Intensity means the field intensity that would exist at a point, in
the absence of waves reflected from the earth or other reflecting objects.
3.13 Service Area as applied to FM broadcast shall refer to the area bounded by a field
intensity that is equal or greater than the minimum value necessary to permit a
desired reception quality in the presence of noise and interference, and from which
the RF Protection ratio is extended.
3.14 Radio-Frequency (R.F.) Protection Ratio is the value of the radio frequency wanted
to interfering signal ratio that enable, under specified conditions, the ratio-frequency
protection ratio to be obtained at the output of a receiver.
3.15 Percentage Modulation as applied to frequency modulations means the ratio actual
frequency swing to the frequency swing defined ad 100 percent modulation,
expressed in percentage. For FM broadcasting station a frequency swing + - 75
kiloHertz defined as 100 percent modulation.
3.16 Multiplex Transmission means the simultaneous transmission of two or more
signals within a single channel. Multiplex transmission as applied to FM broadcast
station, means the transmission of the facsimile or other signals in addition to the
regular broadcast signals.
3.17 Stereophonic Broadcasting Tern
3.17.1 FM Stereophonic Broadcast - The transmission of a stereophonic program by a
single FM broadcast station utilizing the main channel and stereophonic sub
channel.
3.17.2 Main Channel - The band frequencies from 50 to 15,000 Hertz which frequency
modulate to main carrier.
3.17.3 Stereophonic Subchannel - The band of frequencies from 23 to 53 kiloHertz
containing the stereophonic subcarrier and it’s associated sideboards.
3.17.4 Pilot Subcarrier - A pilot subcarrier serving as a control signal for use in the
reception of FM stereophonic broadcasts.
3.17.5 Stereophonic Subcarrier - A stereophonic subcarrier having a frequency which is
the second harmonic of the pilot Subcarrier frequency and which is employed in
FM stereophonic.
3.17.6 Left (or Right) Signal - The electrical output of a microphone or a combination of
microphones placed so as to Convey the intensity, time, and location of sounds
originating predominantly to the listeners left (or right) of the center of the
performing area.
3.17.7 Left (or Right) stereophonic Channel - The left (or Right) signal as electrically
reproduced in the reception of an FM Stereophonic broadcast.
3.17.8 Stereophonic separation - The ratio of the electrical signal caused in the right (or
left) stereophonic channel, to the Electrical signal caused in the left (or right)
stereophonic channel, by the transmission of only a right (or left) signal.
3.17.9 Cross-Talk - An undersigned signal occurring in one channel caused by an
electrical signal in another Channel.
3.18 Experimental Period - The period between 12 midnight to 5:00 a.m. local standard
time (1600-2100 GMT). This period may be used for experimental purposes in testing
and maintaining apparatus by the licensee of any FM broadcast station on its
assigned frequency and not in excess of its authorized power, provided no
interference is caused to other stations maintaining a regular operating schedule
within such period.
38
3.19 Qualified Technician - As applied to FM broadcasting means a person who is
holder of any class of Radio Telephone Operator’s License or its equivalent except
those mentioned in Section 9.4 as issued by the existing regulatory body.
4. ALLOCATION OF FREQUENCIES FOR FM BROADCAST STATIONS
4.1 Channel-designation of FM broadcast frequencies are shown in the table below:
TABLE 1
Channel No. Frequency (MHz) Channel No. Frequency (MHz)
FM-1 88.1 FM-51 98.1
FM-2 88.3 FM-52 98.3
FM-3 88.5 FM-53 98.5
FM-4 88.7 FM-54 98.7
FM-5 88.9 FM-55 98.9
FM-6 89.1 FM-56 99.1
FM-7 89.3 FM-57 99.3
FM-8 89.5 FM-58 99.5
FM-9 89.7 FM-59 99.7
FM-10 89.9 FM-60 99.9
FM-11 90.1 FM-61 100.1
FM-12 90.3 FM-62 100.3
FM-13 90.5 FM-63 100.5
FM-14 90.7 FM-64 100.7
FM-15 90.9 FM-65 100.9
FM-16 91.1 FM-66 101.1
FM-17 91.3 FM-67 101.3
FM-18 91.5 FM-68 101.5
FM-19 91.7 FM-69 101.7
FM-20 91.9 FM-70 101.9
FM-21 92.1 FM-71 102.1
FM-22 92.3 FM-72 102.3
FM-23 92.5 FM-73 102.5
FM-24 92.7 FM-74 102.7
FM-25 92.9 FM-75 102.9
FM-26 93.1 FM-76 103.1
FM-27 93.3 FM-77 103.3
FM-28 93.5 FM-78 103.5
FM-29 93.7 FM-79 103.7
FM-30 93.9 FM-80 103.9
FM-31 94.1 FM-81 104.1
FM-32 94.3 FM-82 104.3
FM-33 94.5 FM-83 104.5
FM-34 94.7 FM-84 104.7
FM-35 94.9 FM-85 104.9
FM-36 95.1 FM-86 105.1
FM-37 95.3 FM-87 105.3
FM-38 95.5 FM-88 105.5
FM-39 95.7 FM-89 105.7
FM-40 95.9 FM-90 105.9
FM-41 96.1 FM-91 106.1
FM-42 96.3 FM-92 106.3
FM-43 96.5 FM-93 106.5
FM-44 96.7 FM-94 106.7
FM-45 96.9 FM-95 106.9
FM-46 97.1 FM-96 107.1
FM-47 97.3 FM-97 107.3
FM-48 97.5 FM-98 107.5
FM-49 97.7 FM-99 107.7
FM-50 97.9 FM-100 107.9
39
5. CLASSES OF STATIONS
5.1 Class-A Stations - shall have an authorized transmitter power not exceeding
25kilowatts.
5.2 Class-B Stations - station shall have an authorized transmitter power not
exceeding 10 kilowatts.
5.3 Class-C Station - station shall have an authorized transmitter power not exceeding
1kilowatts.
5.4 Class-D Station - station shall have an authorized transmitter power not
exceeding 10 watts.
6. TABLE OF ASSIGNMENTS:
6.1 The frequency assignments for the Manila, Laoag, Legazpi, Cebu, Davao, and
Zamboanga shall be selected from TABLE 2.
TABLE 2
Channel No. Frequency (MHz)
FM-2 88.3
FM-6 89.1
FM-10 89.9
FM-14 90.7
FM-18 91.5
FM-22 92.3
FM-26 93.1
FM-30 93.9
FM-34 94.7
FM-38 95.5
FM-42 96.3
FM-46 97.1
FM-50 97.9
FM-54 98.7
FM-58 99.5
FM-62 100.3
FM-66 101.1
FM-70 101.9
FM-74 102.7
FM-78 103.5
FM-82 104.3
FM-86 105.1
FM-90 105.9
FM-94 106.7
FM-98 107.5
7. RADIO FREQUENCY PROTECTION RATIO
7.1 The following radio frequency protection ratios (in table 3 below) provide for the
minimum physical separation between stations and protection of stations from
interference.
TABLE 3
FREQUENCY RADIO-FREQUENCY PROTECTION RATIO (dB)
SPACING
(KHz) MONOPHONIC STEREOPHONIC
Steady Troposheric Steady Troposheric
Interference Interference Interference Interference
0 36 28 45 37
25 31 27 51 43
50 24 22 51 43
75 16 16 45 37
100 12 12 33 25
150 8 8 18 14
200 6 6 7 7
250 2 22 2 2
300 -7 -7 -7 -7
350 -15 -15 -15 -15
400 -12 -20 -20 -20
40
7.1.1 Intermediate frequency amplified of most FM broadcast receivers is designed to
operate on 10.7 megahertz. For this reason the assignment of two stations in the
same area, one with frequency 10.6 or 10.8 megahertz removed from that of the
other, should be avoided if possible.
7.1.2 Stations normally will not be authorized to operate in the same city or in nearby
cities with a frequency separation of less than 800 kHz.
7.1.3 The nature and extent of the protection from interference accorded the FM
broadcast stations is limited solely to that which results from the application of the
radio frequency protection ratio.
8. TECHNICAL REQUIREMENTS
8.1 Safety Requirements
8.1.1 Conformity with Electrical Wiring rule - All equipment electrical installation shall
conform with provision of the Philippine Code and the Philippine electronics Code
so as to ensure the safety of property, equipment, personnel and the public in
general.
8.1.2 Use of Standard Component Parts - All components parts shall be in accordance
with generally accepted standards or those of The FCC or CCIR.
8.2 Transmitting Facilities
8.2.1 Location and Layout
8.2.1.1 Any site particularly suitable for FM broadcasting in an area in the absence
of other comparable Sites may be shared and be made available to as many
applicants as possible.
8.2.1.2 Transmitter Location
8.2.1.2.1 The transmitter location should be as hear the center of the proposed
service area as possible consistent with the applicant’s ability to find a site with
sufficient elevation to provide service throughout the area. The transmitting site
should be selected consistent with the purpose of the station, i.e., whether it is
intended to serve a small city, a metropolitan area, or a large region. The location
should be so chosen that line-of-sight can be obtained from the antenna over the
principal city or cities to be served.
8.2.2 Antenna System
8.2.2.1 It shall be standard to employ horizontal polarization. However, circular or
elliptical polarization of the clockwise or counterclockwise rotation may be
employed, if so desired.
8.2.2.2 The antenna must be constructed so that it is an clear as possible of
surrounding building or object that would cause shadow problems.
8.2.2.3 In the event a common tower is used by two or more licenses for antenna
and/or antenna supporting purposes, the license who owns the tower shall
assume full responsibility for the maintenance of the tower structure, its painting
and lighting requirements. In the event of shared ownership, one license shall
assume such responsibility.
8.2.2.4 When necessary for the protection of air navigation, the antenna and
supporting structure shall assume full responsibility for the maintenance of the
tower structure; its license shall assume such responsibility.
8.2.3 Transmitter and Associated Equipment
8.2.3.1 Electrical Performance Standards
The general design of the FM broadcast transmitting system (from input
terminal of Microphone preamplifier, through audio facilities at the studio through
lines or other between studio and transmitter through audio facilities at the
transmitter, but equalizers for the correction of deficiencies in microphone
response) shall be in accordance with the following principles and specifications:
8.2.3.1.1 The operating power of each station shall be determined by the indirect
method. This is the
Product of the plate voltage (Ep) and the plate current (lp) of the last radio stage
efficiency factor, F; that is:
Operating power = Ep * lp * F
The efficiency factor, F, shall be established by the transmitter manufacturer for
each type of transmitter and shall be specified in the instruction book supplied to
the customer with each transmitter.
8.8.2.3.1.1.1 The transmitter shall operate satisfactorily in the operating power range
with a frequency swing of + - 75 kilohertz which is defined as 100 percent
modulation.
41
8.2.3.1.1.1 The transmitting system shall be capable of transmitting a band of
frequencies from 50 to 15,000 hertz. Pre-emphasis shall be employed in
accordance with the impedance characteristic of a series inductance –
resistance network having a time constant of 75 microseconds. The deviation
of the system response from the standard pre-emphasis curve shall lie
between two limits. The upper of these limits shall be uniform: (no deviation)
from 50 to 15,000 hertz and 3 dB below the upper limit; from 50 to 100 hertz
and the lower limit shall fall from the 3 dB limit at a uniform rate
of 1 dB per octave (4 dB at 50 Hertz); from 7,500 to 15,000 hertz the lower
limit shall fall from the 3 dB limit at a uniform rate of 2 dB per octave (5 dB at
15,000 Hertz).
8.2.3.1.3 At any modulating frequency between 50 to 15,000 Hertz and at
modulation percentages of 25,50 and 100 percent, the combined audio frequency
harmonics measured in the output of the system shall not exceed the root-mean-
square values given in the following table:
Modulating Frequency Distortion Percent
50 to 100 Hertz……………….3.5
100 to 7,500 Hertz……………..2.5
7,500 to 15,000 Hertz……………3.0
8.2.3.1.3.1 Measurement shall be made employing a 75-microsecond de-emphasis in
the measuring equipment and 75-microsecond pre-emphasis in the
transmitting equipment, and without compression, if a compression
amplifier is employed.
8.2.3.1.3.2 It is recommended that none of the three main divisions of the system
(transmitter, studio to transmitter circuit, and audio facilities) contribute
over one-half of these percentages since at some frequencies the total
distortion may become the arithmetic sum of the distortion of the divisions.
8.2.3.1.4 The transmitting system output noise level (frequency modulation) in the
band of 50 to 15,000 Hertz shall be at least 60 decibels below 100 percent
modulation (frequency swing of + - 75 kilohertz). The measurement shall
be made using 400 Hertz modulation as reference. The noise measuring
equipment shall be provided with a standard 75-microsound de-emphasis;
the ballistic characteristic of the instrument shall be similar to those of the
standard VU-meter.
8.2.3.1.5 the transmitting system output noise level (amplitude modulation) in the
band of 50 to 15,000 Hertz shall be at least 50 decibels below the level
representing 100 percent amplitude modulation. The noise measuring
equipment shall be provided with a standard 75-microsecond de-emphasis
and the ballistic characteristics of the instrument shall be similar to those
of the standard VU meter.
8.2.3.1.6 Automatic means shall be provided in the transmitter to maintain the
assigned center frequency within the allowable tolerance of + - 2000
Hertz.
8.2.3.1.7 The transmitter shall be equipped with suitable indicating instruments for
the determination of operating power and with other instrument as are
necessary for its proper adjustments, operation, and maintenance.
8.2.3.1.8 Adequate provisions shall be made for varying the transmitter output
power to compensate for excessive variations in line voltage or for other
factors affecting the output power.
8.2.3.1.9 Allowance shall be provided in all component parts to avoid overheating at
the rated maximum output power.
8.2.3.1.10 If a limiting or compression amplifier is employed, precaution should be
maintained in its connection in the circuit due to the use of pre-emphasis
in the transmitting system.
8.2.3.1.11 Any emission appearing on a frequency removed from the carrier by
between 120 kHz and 240 kHz inclusive shall be attenuated, at least, 25
decibels below the level of the unmodulated carrier.
8.2.3.1.12 Any emission appearing on a frequency removed from the carrier by more
than 240 kHz up to including 600 kHz shall be attenuated at least 35 dB
below the level of the unmodulated carrier.
42
8.2.3.1.13 Any emission appearing on a frequency removed from the carrier by more
than 75 kHz shall be attenuated at 45 + 10 log (power, in watts decibels
below the level of the unmodulated carrier or 80 decibels, whichever is the
lesser attenuation.
8.2.3.2 Construction. In general, the transmitter shall be constructed either on
racks and panels or in totally enclosed frames protected as required by the
Philippine Electronic Code and the Philippine Electrical Code means. All
metallic parts shall be connected to ground.
8.2.3.2.1.1 Enclosure. The transmitter shall be enclosed in a metal frame or grill
separated from the operating space by a barrier or other equivalent
means. All metallic parts shall be connected to ground.
8.2.3.2.1.2 Grounding of controls. All external metallic handles and controls accessible
to the operating personnel shall be effectively grounded. Circuit in excess
of 150 volts shall have any part exposed to direct contact. A complete deed
front type of switchboard is preferred.
8.2.3.2.1.3 Interlocks on doors. All access shall be provided with interlocks, which will
disconnect all voltages in excess of 350 volts when any access door is
opened.
8.2.3.2.2 Means shall provide for making all tuning adjustments, requiring voltage in
excess of 350 volts to be applied to the circuit, from the front of the panels
with all access doors closed.
8.2.3.2.3 Proper bleeder resistors or other automatic means shall be installed across
all capacitors banks to lower any voltage which may remain accessible with
access door is opened.
8.2.3.2.4 All plate supply and other high voltage equipment, including transformers,
filters, rectifiers and motor generators, shall be protected so as to prevent
injury to operating personnel.
8.2.3.2.4.1 Power equipment and control panels of the transmitter shall meet the
above requirements (exposed 220 volts AC switching equipment on the
front of the power control panels is not recommended but is not
prohibited).
8.2.3.3 Wiring and shielding
8.2.3.3.1 The transmitter panels or units shall be wired in accordance with standard
switchboard practice, either with insulated leads properly cabled and
supported or with rigid bus bar properly insulated and protected.
8.2.3.3.2 Wiring between units of the transmitter, with the exception of circuits
carrying radio frequency energy, shall be installed in conduits of fiber or
metal raceways for protection from mechanically injury.
8.2.3.3.3 Circuits carrying radio frequency energy between units shall be wired with
coaxial or two wire balanced lines properly shielded.
8.2.3.3.4 All stages or units shall be adequately shielded and filtered to prevent
interaction and radiation.
8.2.3.4.1 All instruments having more than 1,000 volts potential to ground on the
movements shall be protected by a cage or cover. (Some instruments are
designed by the manufacturer to operate safety with voltages in excess of
1,000 volts on the movement)
8.2.3.4.2 In case the plate voltmeter is located on the low potential side of the
multiplier resistor with the potential of the high potential terminal of the
instrument at or less than 1,000 volts above ground protective case is
required. However, it is good practice to protect voltmeter subject to more
than 5,000 volts with suitable over voltage protective device across the
instrument terminal in case the winding opens.
8.2.3.4.3 Transmission line meters and any other radio frequency instrument which
may be necessary for the operator to read, shall be so installed as to be
easily and accurately read without the operator having to risk contact with
circuits carrying high potential radio frequency energy.
8.2.3.5 Indicating Instruments
8.2.3.5.1 Each FM broadcast station shall be equipped with indicating instruments for
measuring the direct plate voltage and current of the last radio stage and
the transmission line radio frequency power.
8.2.3.5.2 If the defective instruments are a plate voltmeter or plate ammeter in the
last radio stage, the operating power shall be maintained by means of the
radio frequency transmission line-meter.
8.2.4 Stereo Broadcasting
43
8.2.4.1 FM broadcast stations may transmit stereophonic broadcasts, upon proper
authorization from the regulatory agency.
8.2.4.2 The pilot subcarrier frequency shall be checked as often as necessary to
insure that it is kept at all times within the prescribed tolerance of 2 Hertz.
8.2.4.3 Stereophonic Transmission Standards. The modulating signal for the main
channel shall consist of the sum of the left and right signal.
8.2.4.4 A pilot subcarrier at 19, 000 Hertz plus or minus 2 Hz shall be transmitted
that shall frequency modulate main carrier between the limits of 8 and 10
percent.
8.2.4.5 The stereophonic subcarrier shall be the second harmonic of the pilot
subcarrier and shall cross the time axis with a positive slope
simultaneously with each crossing of time axis by the pilot subcarrier.
8.2.4.6 Amplitude modulation of the stereophonic subcarrier shall be used.
8.2.4.7 The stereophonic subcarrier shall be suppressed to a level less than one
percent modulation of the main carrier.
8.2.4.8 The stereophonic subcarrier shall be capable of accepting audio frequencies
from 50 to 15, 000 Hz.
8.2.4.9 The modulating signal for the stereophonic subcarrier shall be equal to the
difference of the left and right signals.
8.2.4.10 The pre-emphasis characteristics of the stereophonic subcarrier shall be
identical with these of the main channel with respect to phase and
amplitude at all frequencies.
8.2.4.11 The sum of the sidebands resulting from amplitude modulation of the
stereophonic subcarrier shall not cause a peak deviation of the main carrier
in excess of 45 percent of total modulation (excluding SCA subcarriers)
when only a left (or right) signal exists; simultaneously in the main
channel, the deviation when only a left (or right) signal exists shall not
exceed 45 percent of total modulation (excluding SCA subcarriers)
8.2.4.12 The maximum modulation of the main carrier by all SCA subcarriers shall
be limited to 10 percent.
8.2.4.13 At the instant when only a positive left signal is applied, the main channel
modulation shall cause an upward deviation of the main carrier frequency,
and the stereophonic subcarrier and its sideband signal shall excess the
time axis simultaneously and in the same direction.
8.2.4.14 The ratio of peak main channel deviation to peak stereophonic subchannel
deviation when only a steady left (or right) signal exists shall be with in
plus or minus 3.5 percent of unity for all levels of this signal and all
frequencies from 50 to 15, 000 Hertz.
8.2.4.15 The phase difference between the zero points of the main channel signal
and the stereophonic subcarrier sidebands envelope, when only a steady
state left (or right) signal exists, shall not exceed plus or minus 3 degrees
for studio modulating frequencies from 50 to 15, 000 Hz.
Note: if the stereophonic separation between left and right stereophonic channels is
better than 29.7 decibels at audio modulating frequencies between 50 to 156, 000 Hz it
will be assumed that 8.2.4.3.11 and 8.2.4.3.12 of this section have been complied with.
8.2.4.16 Cross talk into the main channel caused by a signal in the stereophonic sub
channel shall be attenuated at least 40 decibels below 90 percent
modulation.
8.2.4.17 Cross talk into the stereophonic sub channel caused by a signal in the main
channel shall be attenuated at least 40 decibels below 90 percent
modulation.
8.2.4.18 For required transmitter performance the maximum modulation to be
employed is 90 percent. (Excluding pilot sub carrier) rather than 100
percent. For electrical performance standards of the transmitter and
associated equipment, 100 percent modulation is referred to include the
pilot sub carrier.
8.2.5 Subsidiary Communications Authorization
8.2.5.1 An FM broadcast licensee or permitee may apply for a subsidiary
Communication (SCA) to provide subsidiary services on a multiplex basis.
8.2.5.2 An applicant for SCA shall specify the particular nature or purpose of the
proposed used.
8.2.5.3 Nature of the SCA
44
8.2.5.4 Subsidiary communications multiplex operations; engineering standards.
8.2.5.4.1 Frequency modulation of the SCA subscribers shall be used.
8.2.5.4.2 The instantaneous frequency of SCA subscribers shall at all times be within
the range 20 to 75 kHz; provided however, that when the station is
engaged in stereophonic broadcasting, the instantaneous frequency of SCA
sub carriers shall at all times be within the range 53 to 75 kHz.
8.2.5.4.3 The arithmetic of the modulation of the main carrier by SCA sub carrier
shall not exceed 30 percent; provided however, that when the station is
engaged in stereophonic broadcasting, the arithmetic sum of the
modulation of the main carrier by the SCA sub carriers shall not exceed 10
percent.
8.2.5.4.4 Frequency modulation of the main carrier caused by the SCA sub carrier
operation shall in the frequency range 90 to 15, 000 Hz at least 60 dB
below 100 percent modulation.
8.2.6 Studio Equipment, and Allied Facilities
8.2.7 The studio being the recognized source of program materials and other
forms of intelligence of various kinds and content, must be properly
equipped to faithfully respond to these impressions and reproduce the
same to the highest degree possible, up to the turnover point which is the
transmitter input.
8.2.6.1 Studio Location and Layout
8.2.6.1.1 Each studio shall be associated with a control room from which the
operational area of the studio may be viewed with ease. However, when
the studio and control rooms are integrated into one, an announcer shall
perform simple front panel type functions like level adjustments and
switching during his/her board hours.
8.2.6.1.2 Studios and control rooms shall be so constructed that they are adequately
insulated from sources of extraneous noise and vibration, and the acoustic
treatment of such studios, and control rooms shall be in accordance with
good engineering practice.
8.2.6.1.3 The recommended complement of broadcast equipment for each studio
consist of the following:
8.2.6.1.3.1 Two (2) Microphones of undistorted quality response, preferably of the
unidirectional type which shall pass a relatively flat frequency response
within +/- 2 dB to audio impressions from 50 to 7, 500 Hertz when
referred to 1, 000 Hertz from a source at a distance of from 2 to 6 inches
away.
8.2.6.1.3.2 Two (2) 2-speed or 3-speed type Transcription Turntables capable of
running within +/- 0.3 percent of the standard average rotation speed of
33 1/3 rpm, 45 rpm, 78.26 rpm to avoid objectionable wow and flutter. It
shall also run smoothly so that its associated pick-up and equalizer units
may not reproduce extraneous noise and rumble when a silent groove
record is played therein. The same pick-up and equalizer units shall pass a
relatively flat frequency response within +/- 2 dB to a sweep frequency
range of from 50 to 10, 000 Hertz when referred to 1, 000 Hertz.
8.2.6.1.3.3 Two (2) Audio Tape Playback Machines of either the reel type or the
cartridge/cassette type or one of each type, which shall run within +/-0.2
percent of any one of the standard average tape speeds of 3-1/4 lps, and
15 lps with their associated pick-up heads and amplifiers to pass a
relatively flat frequency response within +/- 2 dB and sweep frequency
range of from 50 to 10, 000 Hertz when referred to 1, 000 Hertz.
8.2.6.1.3.4 One (1) Audio Control Console with at least six (6) faders. Its associated
amplifiers shall pass a relatively flat frequency response of within +/- 2 dB
to an audio frequency range of from 50 to 10, 000 Hertz when referred to
10, 000 Hertz.
8.2.6.1.3.5 One (1) Local Program and one (1) Cue Monitor with associated amplifiers
and speakers that will pass a relatively flat frequency response to within
+/- 2 dB of an audio frequency range of from 50 to 10, 000 Hertz when
referred to 1, 000 Hertz.
8.2.6.1.3.6 One (1) Automatic Level Control and Stabilizer unit that shall pass a
relatively flat frequency response to within +/- 2 dB to an audio frequency
range of form 50 to 10, 000 Hertz when referred to 1, 000 Hertz.
8.2.6.1.3.7 One (1) on-air Monitor Receiver of high sensitivity and selectivity.
45
8.2.6.1.3.8 One (1) Audio Tape Recording Machine of either the reel type or the
cartridge/cassette type of any one of each type which shall run within +/-
0.2 percent of any one of the standard average tape speed of 3 ¼ ips, 7 ½
ips and 15 ips, with their associated pick-up heads and amplifiers to pass a
relatively flat frequency response within +/- 2 dB to a sweep frequency
range of from 50 to 10, 000 Hertz when referred to 1, 000 Hertz.
8.3 Emergency Equipment and Facilities
When a need exists, a back-up transmitter (alternate main and/or
auxiliary) may be installed.
8.3.1 Alternate Transmitter
8.3.1.1 Both the regular and the alternate main transmitters shall be installed in
the same location.
8.3.2 Auxiliary Transmitter
8.3.2.1 auxiliary Transmitter shall be installed in the same location as the regular
main transmitter. However, it may be installed in another location
provided it will not or cause harmful interference to the existing radio
installations.
8.3.2.2 Its operating power may be less but never greater than the authorized
power of the regular main transmitter.
8.3.2.3 The auxiliary transmitter shall be maintained so that it may be placed in
operation at anytime for the following purpose:
8.3.2.3.1 The transmission of the regular program upon failure of the regular
main transmitter.
8.3.2.3.2 The transmission of the program during maintenance or
modification works on the regular main transmitter necessitating
discontinuance of its operation.
8.3.3 Spare Component Parts
In order to cut down times during scheduled on-air operations, a
reasonable variety and number of spare components appropriate to the
equipment installed at the site shall be kept on hand.
8.4 Broadcast Transmission Services
Broadcast Transmission services fall under these three categories:
1) Studio-to-transmitter link (STL)
2) Remote Pick-up Broadcast Station
3) Communications, Coordination, and Control Link
The frequency hands authorized for the above services are as follows:
Frequency Band Allocations
STUDIO TO TRANSMITTER LINK
Band A 310-315 MHz
Band B 734-752 MHz
860-880 MHz
942-952 MHz
REMOTE PICK-UP BROADCAST STATION
Band A 305-315 MHz
Band B 45-451 MHz
Band C 455-456 MHz
COMMUNICATIONS, COORDINATION & CONTROL LINK
Band A 4-12 MHz (non-exclusive)
Band B 26.10-26.48 MHz
Band C 162.235-162.615 MHz
Band D 880-890 MHz
The National Telecommunications Commission shall authorize the employment of
any one or all of these broadcast transmission services to a station depending on
the necessity and availability of frequencies for the purpose. Any AM or FM
station authorized to operate is entitled to use any broadcast transmission
services relevant to the efficient operation of the station where the use of physical
lines or cables is not feasible.
46
9 OPERATING REQUIREMENTS
9.1 Hours of Operation
9.1.1 Minimum Operating Schedule – except Sundays and special holidays the license of
each FM station shall maintain a minimum operating schedule of two-thirds of the
total hours that it is authorized to operate between 6 a.m. and 6 p.m. local
standard time, and two thirds of the total hours it is authorized to operate
between 6 p.m. and midnight local standard time, except in emergencies when,
due to causes beyond the control of the licensee, it becomes impossible to
continue operating, the station may cease operations for a period not exceeding
10 days.
9.1.2 Broadcast outside of the authorized regular operating schedule (as before regular
sign-on schedules and/or beyond the regular sign-off schedules) may be aired
without prior authorization from the appropriate regulatory body provided the
program falls under an emergency category of very important relevance to the
station’s existence. The same information shall be entered in the program and
operating logs at the time the same was aired.
9.1.3 If a permanent discontinuance of operations is being contemplated, then the
licensee shall notify the appropriate regulatory body in writing, at least two (2)
days before the actual discontinuance is affected.
9.2 Other Operating Requirements
9.2.1 the center frequency of each FM broadcast station shall be maintained within +/-
2000 Hertz of the assigned center frequency.
9.2.2 The percentage of modulating shall be maintained as high as possible consistent
with good quality transmission and in no case more than 100 percent on peaks of
frequent recurrence.
9.2.3 The operating power of each station shall be maintained as near as practicable to
the authorized operation power, and shall not exceed the limits of 5 percent above
and 10 percent below the authorizing power, except that in an emergency when it
becomes impossible to operate within the authorized power, the station may be
operated with reduced power.
9.2.3.1 The operating power of each station shall be determined by the indirect
method. This is the product of the plate voltage (Ep) and the plate current (Ip) of
the last radio stage, and an efficiency factor, F, that is,
Operating Power = Ep x lp x F
The efficiency factor, F shall be established by the transmitter manufacturer for
each type of transmitter.
9.2.4 The station equipment shall be so operated, tuned and adjusted that emissions
outside of the authorized channel do not cause harmful interference to the
reception of other radio stations. FM broadcast stations shall maintain the
bandwidth occupied by their emissions in accordance with the specifications set
forth in this section. Stations shall achieve the highest degree of compliance
practicable with their existing equipment. In either case, should harmful
interference to the reception of other radio stations occur, the licensee may be
required to take such further steps as may be necessary to eliminate the
interference.
9.2.5 If a limiting or compression amplifier is employed care should be maintained in its
use due to pre-emphasis in the transmitting system.
9.2.6 Field Strength Contours
9.2.6.1 Application for FM authorizations may show at least the estimated field
strength contour of 50 microvolt per meter (34 dBu) for stations operating on
mono or of 250 microvolt per meter (48dBu) for stations operating on stereo.
These contours indicate only the approximate extent of coverage over average
terrain in the absence of interference. Under actual conditions, the true coverage
may vary greatly from these estimates because the terrain over any specified
path is expected to be different from the average terrain on which the field
strength chart was based. Because of these factors, the estimated contours give
no assurance of service to any specific percentage of receiver locations within the
distance indicated.
9.2.6.2 The field strength contours provided for this section shall be considered for
the following only:
47
9.2.6.2.1 In the estimation of coverage resulting from the selection of a particular
transmitter site by an applicant for an FM broadcast station.
9.2.6.2.2 In the determining the minimum field strength to be provided over the
principal community to be served.
9.3 Posting of Station and Operating Licenses
9.3.1 The station license and other instrument(s) of station authorization shall be
posted in a conspicuous place and in such a manner that all terms are visible, at
the place the licensee considers to be the principal control point of the
transmitter. At all other license and other instrument(s) of station authorization
shall be posted.
9.4 Operator Requirements
9.4.1 Radio Operators holding a valid radiotelephone first class operators license, except
as provided for the transmitting apparatus and shall be on duty either at the
transmitter location or remote control point.
9.4.2 A station which is authorized which is authorized with a power of 10 kilowatts or
less may be operated by persons holding commercial radio operator’s license of
any class, except those with an aircraft radiotelephone operator authorization or a
temporary limited radiotelephone operator class license, when the equipment is so
designed that the stability of the frequency is maintained by the transmitter itself
within the limits of tolerance specified, and none on the operations, except those
specified in sub-paragraph (1) through (4) of this paragraph, necessary to be
performed during the course of normal operation, may cause off-frequency
operation or result in any unauthorized radiation. Adjustments of the transmitting
equipment by such operators, except when under the immediate supervision of a
radiotelephone first class operator, shall be limited to the following:
9.4.2.1 Those necessary to commence or terminate transmitter emission as a
routine matter.
9.4.2.2 These external adjustments that may be required as a result variation of
primary power supply.
9.4.2.3 Those external adjustments which may be necessary to insure modulation
within the limits required.
9.4.2.4 Those adjustments necessary to effect any change in operating power
which may be required by the station’s instrument authorization. Should the
transmitting apparatus be observed to be operating in manner consistent with the
station’s instruments authorizations and one of the above adjustments are
effective in bringing it into proper operations. The person holding other than
radiotelephone first class operator’s license and not acting under the immediate
supervision of a radio-telephone first class operator, shall be required to terminate
the station’s emissions.
9.4.3 A station shall employ at least one full-time first class radio telephone operator
whose primary duty shall be to effect and ensure the proper functioning of the
transmitting equipment.
9.4.4 Log Requirements
The licensee or permitee of each FM broadcast station shall maintain
program and operating logs and shall require entries to be made as follows:
9.5.1 In The Program Log
9.5.1.1 An entry of the time each station identification announcement (call letters
frequency, and location) is made.
9.5.1.2 An entry briefly describing each program broadcast such as “music”
“drama” “speech”, etc. together with the name at the beginning and ending of the
complete program. If a mechanical record is used, the entry shall show the exact
nature thereof, such as “record”, “transcription”, etc. and the time it is announced
as a mechanical record. If a speech is made by a political candidate, the name
and political affiliation of such a speaker shall be entered.
9.5.1.3 An entry showing that each sponsored program broadcast has been
announced as sponsored, a paid for, or furnished by the sponsor.
9.5.1.4 An entry showing, for each program of network origin, t he name of the
network originating the program.
9.5.2 In The Operating Log
9.5.2.1 An entry of the time the station begins to supply power to the antenna and
the time it stops.
9.5.2.2 An entry of the time the program begins and ends.
9.5.2.3 An entry of each interruption to the carrier wave, its cause, and duration;
or an interruption of program transmission.
48
9.5.2.4 An entry of the following every 30 minutes:
9.5.2.4.1 Operating constants of the last radio frequency stage ( total plate current and
plate voltage )
9.5.2.5 Any other entry required by the instrument of authorization.
9.5.3 If a maintenance log is kept aside from the operating log, the following are
recommended.
9.5.3.1.1 An entry of the time and result of test of auxiliary transmitter.
9.5.3.1.2 A notation of all frequency checks and measurements made independently of
the frequency monitor and of the correlation of these measurements with
frequency monitor indications.
9.5.3.1.3 A notation of the calibration checks of automation recording devices. An entry
of the date and time of removal from and restoration to service of any of the
following equipment in the event it becomes defective:
9.5.3.1.3.1 Final R.F. stage plate voltmeter.
9.5.3.1.3.2 Final R.F. stage plate ammeter.
9.5.3.1.4 Transmission line radio frequency voltage, current, or power meter.
9.5.3.1.5 Any other entries required by the current instrument authorization of station
and the provisions of this subpart.
9.5.4 A log must be kept of all operations during the experimental period. If the entries
required above are not applicable thereto then the entries shall be made so as to
fully describe the operations.
9.5.5 Logs of FM broadcast stations shall be retained by the licensee or permitee for a
period of two (2) years: Provided, however, that logs involving communications
incident to a disaster or which include communications incident to or involved in
an investigation by the appropriate regularly body and concerning which the
licensee or permitee has been notified, shall be retained by the licensee or
permitee until he is specifically authorized in writing by the appropriate regulatory
body to destroy them: Provided further, that logs incident to or involve in any
claim or complaint of the licensee or permitee until such claim or complaint has
been fully satisfied or until the same has been barred by the statute limiting the
time for the filing of suits upon such claims.
9.5.6 Each log shall be kept by the person or persons competent to do so, having actual
knowledge of the facts required, who shall sign the log when starting duty and
again when going off duty. The logs shall be made available upon request by an
authorized representative (s) of the appropriate regulatory body during
reasonable hours of the day.
9.5.7 A log shall be kept in an orderly manner, in suitable for, and in such detail that
the data required for the particular class of station concerned are readily
available. Key letters or abbreviation may be used if proper meaning or
explanation is contained elsewhere in the log,
9.5.8 No log or portion thereof shall be erased, obligated, or willfully destroyed within
the period of retention provided by the rules. Any necessary correction may be
made only by the person originating the entry who shall strike out the erroneous
portion, initial the correction. Rough log (s) may be transcribed into condensed
form but in such cases the original rough or memoranda and all portion(s) thereof
shall be preserved and made part of the complete log.
9.6 Operation under Subsidiary Communications Authorization
9.6.1 Operations conducted under a Subsidiary Communications Authorizations (SCA)
shall conform to the uses and purposes authorized by the appropriate regulatory
body in granting the SCA application. Prior permission to engage in any new or
additional activity must be obtained from the appropriate regulatory body
pursuant to application therefore.
9.6.2 Each licensee or permitee shall maintain a daily operating log SC operation in
which the following entries shall be made (excluding sub carrier interruption of
five minutes or les):
9.6.2.1 Time sub carrier generator is turned on.
9.6.2.2 Time modulation is applied to sub carrier.
9.6.2.3 Time modulation is removed from sub carrier.
9.6.2.4 Time sub carrier generator is turned off.
9.6.2.5 An entry describing the results obtained in determining the frequency of
each SCA sub carrier.
9.6.2.5.1 Program and operating logs for SCA operation may be kept in special columns
provided on the station’s regular program and operating log sheet
49
9.7 Remote Control Operation
Operation by remote control shall be subject to the following conditions:
9.7.1 The equipment at the operating and transmitting positions shall be so installed
and protected that it is not accessible to or capable of operation by persons other
than those duly authorized by the licensee.
9.7.2 The control circuits from the operating positions to the transmitter shall provide
positive on and off control and shall be such that open circuits, short circuits,
ground, or other line faults will not actuate the transmitter and any fault causing
loss of such control will automatically place the transmitter in an inoperative
position.
9.7.3 A malfunction of any part of the remote control equipment and associated line
circuits resulting in improper control or inaccurate meter reading shall be cause
for the immediate cessation of operation by remote control.
9.7.4 Control and monitoring equipment shall be installed at the remote control point so
as to allow the license operator to perform all the functions in a manner required
by the rules.
9.8 Station Inspection. The license of any FM broadcast station shall make the station
available for inspection by representatives of the appropriate regulatory body
during reasonable hours of the day.
TECHNICAL STANDARDS AND OPERATING REQUIREMENTS FOR TELEVISION
STATIONS IN THE PHILIPPINES
1 Prediction of Coverage
1.1 All prediction of coverage made pursuant to this section shall be made without regard
to interferences and shall be made only on the basis of estimated field strengths.
1.2 In predicting the distance to the field strength contours, the F(50,50) field strength
chart-figure 1, shall be used. The 50 % field strength is defined as that value
exceeded at 50% of the time. F(50,50) chart gives the estimated 50 percent field
strength exceeded at 50 percent of the locations in decibels 1-microvolt per meter.
The chart is based on an effective power of 1 kilowatt radiated from a half wave
dipole in free space which produces an attenuated field strength at 1.6 kilometers of
about 103 dB above 1-microvolt per meter (137.6 millivolts per meter).
1.3 To use chart for other powers, the sliding scale associated with the chart should be
trimmed and used as the ordinate scale. The sliding scale is placed on the chart with
the appropriate graduation for power in line with the horizontal 40dB line on the
chart. The right of the scale is placed in line with the appropriate antenna height
graduations, and the chart then becomes direct reading (in microvolt per meter and
dB above 1 microvolt per meter for this power and antenna height.) Where the
antenna height is not one of these for which a scale is provided, the signal strength or
distance is determined by interpolation between the curves connecting the equidistant
scale. Dividers may be used in lieu of the sliding scale. In predicting the distance to
the field strength contours, the effective radiated power to be used is the power in
the direction of such areas, the appropriate cervical plane radiated power must, of
course be considered in determining this power.
1.4 The antenna to used with this chart is the height of the radiation center of the
antenna above the average elevation of the terrain, the elevations between 3 and 16
kilometers from the terrain, the elevation between 3 and 16 kilometers from the
antenna site are employed. Profile graphs shall be dawn for eight radials beginning at
the antenna site and extending 16 kilometers there from. The radials should be dawn
for each 45 degrees of azimuth starting with North. At least one radial must include
the principal community to be served, then one or more such radials are dawn in
addition to the eight evenly spaced radials, such additional radials shall not be
employed in computing the antenna height above average terrain. The profile graph
should indicate the topography accurately for each radial, and the graphs should be
plotted with the distance means sea level as the as the ordinate. It is not necessary
to take the curvature, as this factor is taken care of in the chapter showing signal
strength.
The average elevation of the 13-kilometer distances between 3 and 16 kilometers
from the antenna site should than be determined from the profile graph, for each
radial. This may be obtained by averaging a planimeter, or by obtaining the median
elevation (exceeded for 50 percent of the distance) in section and averaging these
values.
50
1.5 In cases where the terrain in one or more directions the antenna site departs widely
from the average elevation of 3 to 16 kilometers sector, the predicted method may
indicate contour distances that are different from what may be expected in practice.
For example, a mountain ridge may indicate the practical limit of service although the
prediction method may indicate others.
2. Definition of terms
2.0 Amplitude Modulation
2.1 Frequency Modulation
2.2 Antenna. a wire conductor or conductor in some form that transmits or receives or
both transmits or receives radio wave.
2.3 Antenna Height above average terrain
2.4 Antenna Power Gain
2.5 Antenna Terminal. An accessible point where the entire antenna including the
distributing system terminates into one feed line at the design characteristic
impedance.
2.6 Aspect Ratio. The ratio of picture width to picture height as transmitted.
2.7 Aural Transmitter. The radio equipment for the transmission of the aural signal only.
2.8 Aural Center Frequency. (1) The average frequency of the emitted wave when
modulated by sinusoidal signal; (2) the frequency of the emitted wave without
modulation.
2.9 Azimuthal Pattern. A plot of the free-space radiated field intensity versus azimuth at a
specified vertical angle with respect to a horizontal plane (relative to smooth earth)
passing through the center of the antenna.
2.10 Blanking Level. The level of the signal during the blanking interval, except the
interval during the scanning synchronizing pulse and the chrominance sub carrier
synchronizing burst.
2.11 Chrominance. The colorimetric differences between any color and a reference
color of equal luminance, the reference color having a specified chromaticity.
2.12 Chrominance Subcarrier. The carrier which is modulated by the chrominance
information.
2.13 Color Transmission. The transmission of color television signals which can be
reproduced with different values of hue, saturation, and luminance.
2.14 Effective Radiated Power. The product of the antenna input power and the
antenna power gain. This product should be expressed in kilowatts and in decibels
above one kilowatt (dBk). (If specified for a particular direction, effective radiated
power is based on the antenna power gain in that direction only).
2.15 Field. Scanning through the picture area once in the chosen scanning of the
alternative lines scanning pattern of two to one, the scanning of the alternative lines
of the picture area once.
2.16 Frame. Scanning all of the picture area once. In the line interlaced scanning of
two to one, a frame consists of two fields.
2.17 Free Space Field Intensity. The field intensity that would exist at a point in the
absence of waves reflected from the earth of other reflecting objects.
2.18 Frequency modulation (FM). A system of modulation where the instantaneous
radio frequency varies in proportion to the instantaneous amplitude of the modulating
signal (amplitude of modulating signal to be measured after pre-emphasis, if used)
and the instantaneous radio frequency is independent of the frequency of the
modulating signal.
2.19 Frequency Swing. The instantaneous departure of the frequency of the emitted
wave from the center frequency resulting from modulation.
2.20 Horizontal Pattern. The azimuthal pattern when the specified vertical angle is
zero.
2.21 Interlaced Scanning. A scanning in which successively scanned lines are spaced an
integral number of line widths, and in which the adjacent lines are scanned during
successive cycles of the field frequency.
2.22 Luminance. Luminous flux emitted, reflected, or transmitted per unit solid angle
per unit projected of the area of the source.
2.23 Monochrome Transmission. The transmission of television signals which can be
reproduce in gradation of a single color only.
2.24 Negative Transmission. Where a decrease in initial intensity causes an increase in
the transmitted power.
2.25 Peak Power. The power a radio frequency cycle corresponding in amplitude to
synchronizing peaks.
51
2.26 Percentage Modulation. As applied to frequency modulation, the ratio of the actual
frequency swing to the frequency swing defined as 100 percent modulation,
expressed in percentage. For the aural transmitter of television broadcast stations, a
frequency swing of +25 kilohertz is defined as 100 percent modulation.
2.27 Polarization. The direction of the electric field as radiated from the transmitting
antenna.
2.28 Reference Black Level. The level corresponding to the specified maximum
excursion of the luminance signal in black direction.
2.29 Reference White Level of the Luminance Signal. The level corresponding to the
specified maximum excursion of the luminance signal in the white direction
2.30 Scanning. The process of analyzing successively, according to predetermined
method, the light values of picture elements constituting the total picture area.
2.31 Scanning Line. A single continuous narrow strip of the picture area containing
highlights, shadows, and halftones, determined by the process of scanning.
2.32 Standard Television Signal. A signal, which conforms to the television
transmission standards.
2.33 Synchronization. The maintenance of one operation in step with another.
2.34 Television Broadcast Band. The frequencies in the band extending from 54 to 890
megahertz (channels 2 through 4), 76 to 88 megahertz (channels 5 and 6), 174 to
216 (channels 7 through 13), and 470 to 890 megahertz (channels 14 through 83).
2.35 Television Broadcast Station. A station in the broadcasting service transmitting
simultaneously visual and aural signals intended to be received by the general public.
ITU defines a television station as a station in the broadcasting service employing a
system of telecommunication for the transmission of transit images of fixed of moving
objects.
2.36 Television Channels. A band of frequencies 6-megahertz wide in the television
broadcast band and designed either by number or by the extreme lower and upper
frequencies.
2.37 Television Transmission Standards. The standard which determines the
characteristics of a television signal as radiated by a television broadcast station.
2.38 Television Transmitter. The radio transmitter or transmitters for the transmission
of both visual and aural signals.
2.39 Vertical Pattern. A plot of free space radiated field intensity measured in the
fraunhofer region versus vertical angle in any specified vertical place which contains
the center of the antenna and the center of the earth. The Fraunhofer region, or “far
field” as usually defined, extends beyond a point where the distance between the
transmitting and receiving point as 2A where A is the length of the radiating portion
of the antenna.
2.40 Vestigial Sideband Transmission. A system of transmitting wherein one of the
generated sidebands is partially attenuated and radiated only in part.
2.41 Visual Transmitter. The radio equipment of the carrier, which is modulated by the
picture information.
2.42 Visual Transmitter. The radio equipment for the transmitting a standard television
signal only.
2.43 Visual Transmitter Power. The peak power output when transmitting a standard
television signal.
3. RADIATED SIGNAL CHARACTERISTICS
3.1 Television Channels
The channels allocated for the broadcasting in the Philippines are shown in the
following Tables:
3.1.1 Table 1- VHF- Television Channels
Channel Number Frequency Limits Visual Carrier Aural Carrier
(MHz) Frequency(MHz) Frequency (MHz)
2 54-60 55.250 59.750
3 60-66 61.250 65.750
4 66-72 67.250 71.750
5 76-82 77.250 81.750
6 82-88 83.250 87.750
7 174-180 175.250 179.750
8 180-186 181.250 185.750
9 168-192 187.250 191.750
10 192-198 193.250 197.750
52
11 198-204 199.250 203.750
12 204-210 205.25 209.750
13 210-216 211.250 215.750
3.1.2 Table 2- UHF- Television channels
Channel Number Frequency Limits Visual Carrier Aural Carrier
(MHz) Frequency (MHz) Frequency (MHz)
14 470-476 471.25 475.75
15 476-482 477.25 481.75
16 482-488 483.25 487.75
17 488-494 498.25 493.75
18 494-500 495.25 499.75
19 500-506 501.25 505.75
20 506-512 507.25 511.75
21 512-518 513.25 517.75
22 518-524 519.25 523.75
23 524-530 525.25 529.75
24 530-536 531.25 535.75
25 536-542 537.25 541.75
26 542-548 543.25 547.75
27 548-554 549.25 553.75
28 554-560 555.25 559.75
29 560-566 561.25 565.75
30 566-572 567.25 571.75
31 572-578 573.25 577.75
32 578-584 579.25 583.75
33 584-590 585.25 589.75
34 590-596 591.25 595.75
35 596.602 597.25 601.75
36 602-608 603.25 607.75
37 608-614 609.25 613.75
38 614-620 615.25 619.75
39 620-626 621.25 625.75
40 626-932 627.25 631.75
41 632-638 633.25 637.75
42 638-644 639.25 643.75
43 644-650 645.25 649.75
44 650-656 651.25 655.75
45 656-662 657.25 661.75
46 662-668 663.25 667.75
47 668-674 669.25 673.75
48 674-680 675.25 679.75
49 680-686 681.25 685.75
50 686-692 687.25 691.75
51 692-698 693.25 697.75
52 698-704 699.25 703.75
53 704-710 705.25 709.75
54 710-716 711.25 715.75
55 716-722 717.25 721.75
56 722-728 723.25 725.75
57 728-734 729.25 733.75
58 734-740 735.25 739.75
59 740-746 741.25 745.75
60 746-752 747.25 751.75
61 752-758 753.25 757.75
62 758-764 759.25 763.75
63 764-770 765.25 769.75
64 770-776 771.25 775.75
65 776-782 777.25 781.75
66 782-788 783.25 787.75
67 788-794 789.25 793.75
68 794-800 795.25 799.75
69 800-806 801.25 811.75
53
70 806-812 807.25 811.75
71 812-818 813.25 817.75
72 818-824 819.25 823.75
73 824-830 825.25 829.75
74 830-836 831.25 835.75
75 836-842 837.25 841.75
76 842-848 843.25 847.75
77 848-854 849.25 853.75
78 854-860 853.25 859.75
79 860-866 861.25 865.75
80 866-872 867.28 871.75
81 872-878 873.25 877.75
82 878-884 879.25 883.75
83 884-890 885.25 889.75
3.2 Channel and Carrier Frequency Locations
The bandwidth of television broadcast channels shall be 6 MHz. The visual
carrier frequency shall be 1.25 MHz above the lower frequency limit of the channel
and the unmodulated aural carrier frequency shall be 4.5 MHz above the visual
carrier or 0.25 MHz below the upper frequency limit of the channel.
Frequency offsets from he visual carrier frequency may be prescribed by the NTC.
3.3 Visual Carrier Modulation
The visual carrier shall be amplitude modulated by the video signal.
Negative modulation shall be employed, that is, a decrease in brightness shall
cause an increase in mean visual carrier amplitude.
3.4 Modulation Levels of the Visual Carrier
Blanking level shall correspond to 75 + 2.5 percent of the peak visual
carrier amplitude. Black level shall be independent of light and shade in the
picture. Reference white level shall correspond to 12.5 + percent of the peak
visual carrier amplitude.
3.5 Aural Carrier Modulation
The aural carrier shall be frequency modulated to a maximum frequency
deviation of + 25 kHz by the audio signal
3.6 Polarization of the Radiated Signals
The polarization of the radiated signals from both aural and visual
transmitters shall be the same. It shall be standard to employ horizontal
polarization. However, circular and elliptical polarization of the clockwise and
counterclockwise rotation may be employed if so desired.
4.0 VIDEO CHARACTERISTICS
4.1 Scanning
4.1.1 Aspect Ratio
The aspect ratio of the television picture shall be four (4) units horizontally to
three (3) units vertically.
4.1.2 Scanning Sequence
During active scanning intervals it shall be normal to scan the scene from
left to right horizontally, and from top to bottom vertically, at uniform velocities.
4.1.3 Number of Line or Interlace
For monochrome and color transmission the number of scanning lines per
frame shall be 525, interlaced to one in successive fields.
4.1.4 Chrominance Sub carrier Frequency
The chrominance sub carrier frequency shall be 3.579545 MHz + 10 Hz
with a maximum rate of change not to exceed one-tenth (1/10) Hertz per second.
4.1.5 Horizontal Scanning Frequency
The horizontal scanning frequency shall be 2/455 times the chrominance
sub carrier frequency; this corresponds to 15,750 Hz for monochrome
transmissions and 15,734.264 + 0.044 Hz for color transmissions.
4.1.6 Vertically Scanning Frequency
The vertical scanning frequency is 2/525 times the horizontal scanning
frequency; this corresponds to 60 Hz for monochrome transmission and 59.94 Hz
for color transmissions.
4.2 Video Signal
4.2.1 For monochrome transmission, the transmitter output shall vary in substantially
inverse logarithmic relation to the brightness of the subject.
54
4.2.2 The color picture signal shall correspond to a luminance component transmitted as
amplitude modulation of the picture carrier and a simultaneous pair of
chrominance components transmitted as the amplitude modulation sidebands of
suppressed sub-carriers in quadrature.
4.3 Modulation of Carriers
4.3.1 A carrier shall be modulated within a single television channel for both picture and
synchronizing signals. For monochrome transmission, the two signals comprise
different modulated ranges in amplitude, in accordance with the charts
designated. For color transmission, the two signals comprise different modulation
in amplitude except where the chrominance penetrate the picture region, in
accordance with the charts designated.
4.4 Equation of Complete Color Signal is:
EM = EY‘ + [ EQ’ sin(ωt + 330) + EI cos(ωt + 330) ]
4.4.1 The color picture signals have the following composition:
EQ’ = + 0.41 ( EB’- EY‘) + 0.48(ER’- EY’)
EI’ = - 0.27 ( EB’- EY‘) + 0.74(ER’- EY’)
EY’ = + 0.30ER’ + 0.59EG’ + 0.11EB’
The Color difference frequencies below 500 kHz, the signal can be represented by:
EM = EY‘ + { 1/1.14 [ 1/1.78 (EB’- EY‘) sinωt + (ER‘- EY‘) cosωt ]}
4.4.2 The symbols in subdivision (4.4.1) of this sub-paragraph have the following
significance:
EM‘ is the total video voltage, corresponding to the scanning of a particular
picture element, applied to the visual transmitter.
EY’ is the gamma-corrected voltage of monochrome (black and white) of
the color picture signal, corresponding to the given picture element.
NOTE: Forming of the high frequency portion of the monochrome signal in a
different manner is permissible and may be fact be desirable in order to improve
the sharpness on saturated colors.
EQ’ and E1’ are the amplitude of two orthogonal components of the
chrominance signal corresponding respectively to narrow-band and wide-band
axes.
ER’, EG’ and EB’ are the gamma-corrected voltages corresponding to red,
green and blue signals during the scanning of the given picture element.
W is the angular frequency and is 2 pi times the frequency of the
chrominance subcarrier.
The portion of each expression between brackets in (4.4.1) represents the
chrominance subcarrier signal which carries the chrominance information.
The pass reference in the EM equation in (4.4.1) is the phase of the burst,
+180 deg. The burst corresponds to amplitude modulation of a continuous sine
wave.
4.4.3 The equivalent bandwidth assigned prior to modulation to the color difference
signal EQ1 and are as follows:
Q-channel bandwidth:
At 400 kHz less than 2 dB down.
At 500 kHz less than 6 dB down.
At 600 kHz at least 6 dB down.
I-channel bandwidth:
At 1.3 MHz less than 2 dB down.
At 3.6 MHz at least 20 dB down.
55
4.4.4 The gamma corrected voltages ER’, EG’, and EB’ are suitable for a color picture
tube having primary colors with the following chromaticity in the CIE system of
specifications.
X Y
Red (R) …………………….. 0.67 0.33
Green (G)………………….. 0.21 0.71
Blue (B)…………………….. 0.14 0.08
and having a transfer gradient (gamma exponent) of 2.2 associated with each
primary color. The voltages ER1, EG1, and EB’ may be respectively of the form
ER1/ , EG1/ and EB1/ although other forms may be used with advances in the state
if the art.
NOTE: At the present state of the art it is considered inadvisable to set a
tolerance on the value of gamma and correspondingly this portion of the
specification will not be enforced.
4.4.5 The radiated chrominance subcarrier shall vanish on the reference white of the
scene.
NOTE: The numeral values of the signal specification assume that the
condition will be reproduced as CIE lluminant C (x = 0.310, y = 0.316).
4.4.6 EY’, EG’, ET’ and the components of these signals shall match each other in time to
0.05 microseconds.
4.4.7 The angles of the subcarrier measured with respect to the burst phase, when
reproducing saturated primaries and their components at 75 percent of full
amplitude, shall be within +10 and their amplitudes shall be within +20 percent of
the values specified above. The ratios of the measured amplitudes of the
subcarrier to the luminance signal for the same saturated primaries and their
complements shall fall between the limits of 0.8 and 1.2 of the values specified for
their ratios. Closer tolerances may prove to be practicable and desirable with
advances in the art.
4.5 Color Synchronization
A burst of 8-cycles minimum of the color subcarrier frequency shall occur
during each line blanking period, commencing 5.1428 microseconds after the half
amplitude point in the leading edge of the line synchronizing pulse, At the point
of encoding, the peak to peak amplitude of the subcarrier burst shall be 40
percent of the blanking to reference white signal amplitude and thereafter the
amplitude and phase of the burst shall be preserved relative to that of the
chrominance signal. The envelope of the subcarrier burst signal shall have a
build-up time consistent with the bandwidth restriction of the color difference
signals
4.6 Special Signals in the Field Blanking Interval
4.6.1 The interval beginning with the last 12 microseconds of the line 17 and continuing
through line 20 of the vertical blanking interval of each field may be used for the
transmission of test signals subject to the condition set forth below. Test signals
may include signals used to supply reference modulation levels so that variations
in light intensity of the scene viewed by the camera will be faithfully transmitted;
signals designed to check the performance of the overall transmission sytem or its
individual components, and cue and control signals related to the operation of the
television broadcast station.
4.6.1.1 Modulation of the television transmitter by such signals shall be confined to
the area between the reference white level and the level except where such test
signals are composed of chrominance subcarrier frequencies, in which case their
negative excursions may extent into the synchronizing peak amplitude. In no
case may be modulation excursions produced by test signals extent beyond peak-
of-sync level.
4.6.1.2 The use of test signals shall not result in significant degradation of the
program transmissions of the television broadcast station nor create emission
components in excess of these permitted for normal program transmission.
4.6.1.3 Test signals may not be transmitted during that portion of each line
devoted to horizontal blanking.
56
4.6.1.4 A guard interval of no less than one-half line shall be maintained at all
times between the last test signal and the beginning of the first picture scanning
line.
4.6.2 The intervals within the first and last 10-microseconds of lines 21 through 23 and
microseconds of lines 21 through 23 and 260 through 262 (on a field basis) may
contain coded patterns for the purpose of electronic identification of television
broadcast programs and spot announcements. No single transmission of such
coded pattern shall exceed one second in duration. The transmission of these
patterns shall not result in significant degradation of broadcast transmission.
5. PRIMARY COLOR SIGNAL
5.1 The gamma corrected voltage ER’, EG’ and EB are suitable for a color picture tube
having primary colors with the following chromaticities in the CIE system of
specification:
X Y
Red (R) …………………….. 0.67 0.33
Green (G)………………….. 0.21 0.71
Blue (B)…………………….. 0.14 0.08
and having a transfer gradient (gamma exponent) of 2.2 associated with each
primary color. The voltages ER’, EG’, and EB’ may be respectively of the form ER1/
, EG1/ and EB1/ although other forms may be used with advances in the state if
the art.
NOTE: At the present state of the art it is considered inadvisable to set a
tolerance on the value of gamma and correspondingly this portion of the
specification will not be enforced.
6. TRANSMITTER CHARACTERISTICS
6.1 Visual Transmitter
6.1.1 For monochrome transmission only the overall attenuation characteristics of the
transmitter, measured in the antenna transmission line after the vestigial
sideband filter (if used), shall not be greater than the following amounts below the
ideal demodulated curve.
2 dB at 0.5 MHz
2 dB at 1.25 MHz
3 dB at 2.00 MHz
6 dB at 3.00 MHz
12 dB at 3.5 MHz
The curve shall be substantially smooth between these specified points,
exclusive of the region from 0.75 to 1.25 MHz. Output measurements shall be
made with the transmitter operating to a dummy load of pure resistance and the
demodulated voltage measured across this load. Stations operating of Channels
15-83 and employing a transmitter delivering maximum peak visual power output
of 1-kilowatt or less will not be required to comply with the provisions of this
paragraph.
6.1.2 For color transmission, the saturated given by the paragraph 6.1.1 applies except
as modified by the following:
A sine wave of 3.58 MHz introduced by those terminals of the transmitter
which are normally fed the composite color picture signal shall produce a radiated
signal having an amplitude (as measured with a diode on the R.F. transmission
line supplying power to the antenna), which is down 6 + 2dB with respect to a
signal produced by a sine wave of 200 kHz.
In addition, the amplitude of the signal shall not vary by more than + 2dB
between the modulating frequencies of 2.1 and 4.18 MHz. Stations operating of
Channels 15-83 and employing a transmitter delivering maximum peak visual
power output of 1-kilowatt or less will not be required to comply with the
provisions of this paragraph.
57
6.1.3 The field strength or voltage of the lower sideband, as radiated or dissipated shall
not be greater then 20 dB for a modulating frequency of 1.25 MHz or greater and
in addition for color, shall not be greater than –42 dB for a modulating frequency
of 3.579545 MHz (the color sub-carrier frequency). For both monochrome and
color, the field strength or voltage of the upper sideband as radiated or dissipated
shall not be greater than –20 dB for a modulating frequency of 4.75 MHz or
greater.
For stations operating of Channels 15-83 and employing a transmitter
delivering maximum peak visual power output of 1-kilowatt or less, the field
strength or voltage of the upper and lower sidebands, as radiated or dissipated
shall not depart from the visual amplitude characteristic by more than the
following amounts.
- 2 dB at 0.50 MHz below visual carrier frequency;
- 2 dB at 0.50 MHz above visual carrier frequency;
- 2 dB at 1.25 MHz above visual carrier frequency;
- 3 dB at 2.0 MHz above visual carrier frequency;
- 6 dB at 3.0 MHz above visual carrier frequency;
- 12 dB at 3.5 MHz above visual carrier frequency;
- dB at 3.58 MHz above visual carrier frequency (for color transmission only).
NOTE: Field strength measurements are desired. It is anticipated that
these may not yield data which are consistent enough to prove compliance with
the attenuation standards prescribed above. In that case, measurements with a
dummy load of pure resistance, together with data on the antenna characteristics,
shall be taken in place of overall field measurements.
6.1.4 A sine wave, introduced at those terminals of those terminals of the transmitter
which are normally fed the composite color picture signal, shall produce a radiated
signal having an envelope delay, relative to the average envelope delay, between
0.05 and 0.20 MHz , of zero microsecond up to a frequency of 3.0 MHz; and then
linearly decreasing to 4.18 MHz so as to be equal to –0.17 microsecond at 3.58
MHz. The tolerance on the envelope delay shall be + 0.05 microsecond at 3.58
MHz. The tolerance shall increase linearly to + 0.1 microsecond down to 2.1 MHz,
and remain at + 0.1 microsecond down to 0.2 MHz. (Tolerance for the interval of
0.0 to 0.2 MHz are not specified at the present time). The tolerance shall also
increase linearly to + 0.1 microsecond at 4.18 MHz.
6.1.5 The ratio frequency signal, as radiated, shall have an envelope as would be
produced by a modulating signal in conformity given figures modified by vestigial
sideband operation specified in the given figure.
6.1.6 The time interval between the leading edges of successive horizontal pulses shall
vary less than one half of one percent of the average interval. However, for color
transmission, paragraph 4.1.3 – 4.1.6 shall be controlling.
6.1.7 The rate of change of the frequency of recurrence of the leading edges of the
horizontal synchronizing signals shall not be greater than 0.150 percent per
second, the frequency to be determined by an averaging process carrier out over
a period of not less than 20, nor more than 100 lines, such lines not to include
any portion of the blanking interval. However, for color transmission, paragraph
4.1.3 – 4.1.6 shall be controlling.
6.1.8 For color transmission, the transfer characteristic (that is the relationship between
the transmitter RF output and video signal input) shall be substantially linear
between the reference black and reference white levels.
6.1.9 The maximum phase difference with respect to burst for any brightness level
between 75% and 15% at sync using 10% sub carrier modulation shall be + 10%.
6.1.10 The maximum variation in amplitude of a 3.58 MHz sine wave modulating signal
as the brightness is varied between 75% and 15% at sync peak using 10% sub
carrier modulation depth shall be within + 20% from the ideal.
6.1.11 AM noise measured in root mean square with respect to peak of sync power within
the band of 30 Hz to 4.2 MHz shall be –50 dB or better.
6.1.12 Harmonic radiation in the transmitter output (or after the vestigial sideband filter,
if used) shall be attenuated at least 80 dB.
6.1.13 The carrier frequency shall be within + 1-kilohertz of the authorized frequency.
6.2 Aural Transmitter
6.2.1 The transmitter shall operate satisfactorily with a frequency swing of + 25 kHz,
which is considered 100 percent modulation. It is recommended, however, that
58
the transmitter be designed to operate satisfactorily with a frequency swing of at
least + 40 kHz.
6.2.2 The transmitting system (from input terminals of microphone pre-amplifier
through audio facilities of the studio, through telephone lines or other circuits
between studio and transmitter, through audio facilities at the transmitter but
excluding equalizers for the correction of deficiencies in microphone response)
shall be capable of transmitting a band of frequencies from 50 to 15,000 Hz. Pre-
emphasis shall be employed in accordance with the impedance frequency
characteristics of series inductance-resistance network having a time constant of
75 microseconds. The deviation of the system response from the standard pre-
emphasis curve shall lie between two limits. The upper of these limits shall be
uniform (no deviation) from 50-15,000 Hz. The lower limit shall be uniform from
100-7,500 Hz and 3-dB below the upper limit; from 100 to 50 Hz the lower limit
at a uniform rate of 1-dB per octave (4 dB at 50 Hz); from 7,500 to 15,000 the
lower limit shall fall from 3-dB limit at a uniform rate of 2-dB per octave (5 dB at
15,000 Hz).
6.2.3 At any modulation frequency between 50 and 15,000 Hz at 100% modulation, the
audio frequency harmonics measured in the output of the system shall not exceed
the root-mean square value of 1%.
6.2.4 The transmitting system output noise level (frequency modulation) in the band of
50 to 15,000 Hz shall be at least 55 dB below the audio frequency level
representing a frequency swing of + 25 kHz.
6.2.5 The transmitting system output noise level (amplitude modulation) in the band of
50 to 15,000 Hz shall be at least 50 dB below the level representing 100 percent
amplitude modulation.
6.2.6 Harmonics radiation in the transmitter output (or after the vestigial sideband
filter, if used) shall be attenuated at least 80 dB.
6.2.7 The carrier frequency 4.50 MHz above the actual visual carrier frequency shall be
maintained within + 1-kilohertz.
6.2.8 The power of the aural transmitter shall be 10% but not greater than 20% of the
peak sync power of the visual transmitter.
6.3 Transmitter Construction
6.3.1 In general, the transmitter shall be mounted either on racks and panels or in
totally enclosed frames protected as required by article 810 of the Philippine
Electrical Code and the Philippine Electronics Code and those set forth below:
6.3.2 The transmitter shall be enclosed in a metal frame or grille, or separated from the
operating space by a barrier or other equivalent means. All metallic parts shall be
connected to the ground.
6.3.3 All external metallic handles and controls accessible to the operating personnel
shall effectively grounded. No circuit in excess of 150 volts shall have any part
exposed to direct contact. A complete dead-front type of switchboard is
preferred.
6.3.4 All access doors shall be provided with interlocks which will disconnect all voltages
in excess of 350 volts when any access door is opened.
6.3.5 Means shall be provided for making all tuning adjustments, requiring voltages in
excess of 350 volts to be applied to the circuit, from the front of the panels with
all access doors closed.
6.3.6 Proper bleeder resistors or other automatic means shall be installed across all the
capacitor banks to lower any voltage which may remain accessible with access
door open to less than 350 volts within two seconds after the access door is
opened.
6.3.7 All plate supply and other high voltage equipment, including the transformers,
rectifiers and motor generators, shall be protected so as to prevent injury to
operating personnel.
6.3.8 Commutators guards shall be provided on all high voltage rotating machinery.
Coupling guards should be provided on motor generators.
6.3.9 Power equipment and control panels of the transmitters shall meet the above
requirements (exposed 220 volt A.C. switch equipment on the front of the power
control panels is not recommended but is not prohibited).
6.4 Additional Requirements Applicable both for Visual and Aural Transmitters.
6.4.1 The transmitters shall be equipped with suitable indicating instruments for the
determination of operating power and with other instruments necessary for proper
adjustment, operation, and maintenance of the equipment.
59
6.4.2 Adequate provisions shall be made for vary-the output of the transmitters to
compensate for excessive variations in line voltage or for other factors affecting
the output power.
6.4.3 Adequate provisions shall be provided in all component parts to avoid overheating
at the rated maximum output powers.
6.4.4 All component parts shall be n accordance with general accepted standards or
those of the FCC or CCIR.
6.5 Transmitter Installation
6.5.1 The installation of transmitting equipment shall be made in suitable quarters.
6.5.2 Suitable facilities shall be provided for the welfare and comfort of the operator.
6.5.3 All transmitting equipment electrical installations shall conform with the provisions
of the Philippine Electrical Code and the Philippine Electronics Code so as to assure
the safety of property, equipment, personnel and the public in general.
7. SEPARATIONS
7.1 The provisions of this section relate to physical separations between stations. All
applications for new television broadcast stations or for changes in the transmitter
sites of existing stations shall comply with the following requirements:
7.1.1 Minimum Co-Channel Physical Separation Between Stations:
Channels 2-13 Channels 14-83
300 kilometers 250 kilometers
7.1.2 Minimum Adjacent Channel Physical Separation Between Stations:
Channels 2-13 Channels 14-83
100 kilometers 90 kilometers
7.1.2.1 Due to the frequency spacing which exists between Channels 4 and 5,
between Channels 6 and 7, and between Channels 13 and 14, the minimum
adjacent channel physical separations specified above shall nor be applicable to
these pairs of channels.
7.1.2.2 The physical separation between stations shall be determined by the
airplane distance between the coordinates of their respective transmitter sites.
Exceptions to the minimum physical separations between co-channel or adjacent
stations on a case-to-case basis are stations whose signals are attenuated by the
nature of intervening terrain.
8. PROTECTION FROM INTERFERENCE
8.1 The nature and extend of the protection from interference accorded to television
broadcast stations is limited solely to the protection which results from the
minimum physical separations between stations and the rules and regulations
with respect to maximum power and antenna heights set forth.
9. POWER AND ANTENNA HEIGHT REQUIREMENTS
9.1 Minimum Requirements
The minimum visual effective radiated power in any horizontal direction
shall be –10 dBk (100 watts). No minimum antenna height above average terrain
is specified.
9.2 Maximum Power
9.2.1 The maximum effective radiated powers of television broadcast stations operating
in the channel set forth below with antenna heights not in excess of 600 meters
above average terrain shall be as follows:
Channel Nos Maximum visual effective radiated power
in dB above one kilowatt (dBk)
2 – 6 20 dBk (100 kW)
7 - 13 25 dBk (316 kW)
14 – 83 37 dBk (5000 kW)
60
9.2.2 The maximum effective radiated power (ERP) in any horizontal direction may not
exceed the maximum values permitted by this section. For antenna heights in
excess of 600 meters above average terrain, the power limitation in relation to
height is indicated by the graph.
9.2.3 In Metro-Manila and Metro-Cebu, the maximum effective radiated power of 350
kW for Channels 2-6, and 1,000 kW for Channels 7-13 shall be allowed.
9.2.4 In the computation of the power output of a broadcast station expressed in ERP,
only the output related to the maximum radiation lobe shall be considered.
10. TELEVISION BROADCAST ANTENNA
10.1 Introduction
Television antennas must have the proper performance characteristics over
each channel with a radiation pattern suitable for the population distribution in the
vicinity of the antenna so as to provide adequate field strength for television
service.
10.2 Antenna Specifications
10.2.1 Gain of an Antenna: The gain of an antenna is the ratio of the power required at
the input of a reference antenna to the power supplied to the input of the given
antenna to produce, in a given direction, the same field at the same distance.
When not specified otherwise, the figure expressing the gain of an antenna refers
to the gain in the direction of the radiation of the main lobe. In services using
scattering modes of propagation the full gain of an antenna may not be realizable
in practice and the apparent gain may vary with time.
10.2.2 Beam Tilt: Beam tilt is necessary to bring the main vertical beam tangential to
the earth, which is curving away from it. To accomplish this for a 300 meters
elevation, a beam tilt of about 0.50 is a required. The beam tilt for other heights
can be calculated from the relationship:
Beam tilt angle = 0.02771 Height (in meters) over service area
10.2.3 Power Capability: Power in TV systems shall be expressed in terms of “Peak TV
Power”’ which is the instantaneous power developed in the peak of the
synchronizing pulse of the visual transmitter. Since the black level signal is 0.75
of the total voltage value of the pulse, the black level power (for a totally black
picture) is (0.75)2 or 0.5625. The duty cycle of the synchronizing pulse, both
horizontal and vertical, adds about 4 percent to this power so that black level
power is 0.6 to the peak TV power. Since the aural FM transmitter is usually 0.2
of the peak TV power, the total heating or CW power in a TV signal is 0.8 of the
peak TV power.
Transmission line power shall stated in terms of CW power for unity VSWR
values unless otherwise specified and will, hence, require a power capability of 0.8
of the peak TV power.
The antenna power rating shall also be given in terms of peak TV power
including the 0.2 aural power. The antenna power rating shall however make an
allowance for the VSWR which is likely to be encountered inside the antenna.
Actually, the long transmission lines usually encountered in TV service
attenuate the input power to a lower value so that for an 80 percent line
efficiency, the antenna requirement will only be 80 kW for a 100 kW transmitter.
10.2.4 Beam Width: The angular width of the main beam of the antenna is directly
related to the gain although this may vary somewhat with the method of pattern
synthesis. For most hull-filled antennas, the beam width at half-power or 0.707
voltage point is 58.3 divided by the gain at zero (0)-degree beam tilt and no null
fill. Thus, for a vertical gain of 24, it would be about 2.40 and for a gain of 42 it
would be about 1.40.
10.2.5 Vertical Pattern: Is usually shown as a plot on a rectangular coordinate paper of
relative voltage versus depression angle below the horizon.
The depression angle below the horizon which required null fill, can be
calculated approximately by the following relationship:
61
Depression angle = 0.0576 x height of antenna (meters)
kilometers to the nearest population
10.2.6 Antenna Input Impedance:
The primary purpose of an input impedance specification is to obtain a
good match to the transmission line which carries the power up to the antenna. If
the mismatch is too great, the reflected power may be of such magnitude that it
travels back to the transmitter where it is generally reflected back to the antenna
and appears as a secondary image on the television picture. The image is delayed
by twice the length of the transmission line.
If any case, the specification for the pulse reflection value shall not be
greater than 3 percent of the incident voltage. However, for design purposes, the
Voltage Standing Wave Ratio (VSWR) across the channel may be used as a
guideline. Due to the concentration of energy at the picture carrier and ¾ MHz
above, the VSWR values could be kept fairly low in this region, preferably below a
VSWR of 1.05 at visual carrier.
11. TELEVISION AUXILIARY BROADCAST SERVICES
11.1 Television auxiliary Broadcast Services fall under these categories:
11.1.1 Television pick-up station. A land mobile station used for the transmission of
television program material and related communications from the scenes of
events occurring at points removed from television broadcast station studios to
television broadcast station.
11.1.2 Television STL station (studio-transmitter link). A fixed station used for the
transmission of television program material and related communications from the
studio to the transmitter of a television broadcast station.
11.1.3 Television intercity relay station. A fixed station used for intercity transmission of
television program material and related communications for use by television
broadcast stations.
11.1.4 Television translator relay station. A fixed station used for relaying the signals of
television broadcast stations to television broadcast translator stations.
11.2 Frequency band Allocation
The following frequencies are available for assignment to television pickup,
television STL, and television intercity relay stations:
BAND A BAND B BAND D MH/z
MH/z MH/z
1990-2008 6875-6900 12700-12725 1227-13000
2008-2025 6900-6925 12725-12750 13000-13025
2025-2042 6925-6950 12750-12775 13025-13050
2042-2059 6950-6975 12775-12800 13050-13075
2059-2076 6975-7000 12800-12825 13075-13100
2076-2093 7000-7025 12825-12850 13100-13125
2093-2110 7025-7050 12850-12875 13125-13150
2450-2467 7050-7075 12875-12900 13150-13175
2467-2484 7075-7100 12900-12925 13175-13200
2484-2500 7100-7125 12925-12950 13200-13225
12950-12975 13225-13250
The National Telecommunication Commission shall authorize the
employment of any one or all of these television auxiliary broadcast services to a
station depending of the necessity and availability of frequencies for the purpose.
Any station authorized to operate is entitle to use any television auxiliary
broadcast services relevant to the efficient operation of the station where the use
of physical lines or cables is not feasible.
62
6543210
0.2 0.75 1.25 4.2 4.5
RECTIFIED
OUTPUT
MODULATING FREQUENCY (MHZ)
IDEAL DEMODULATED AMPLITUDE CHARACTERISTIC OF TELEVISION TRANSMITER
0.5
1.0
RELATIVE
MAXIMUM
RADIATED
FIELD
STRENGTH
(PICTURE
CARRIER= 1.0)
CHANNEL FREQUENCY SPECTRUM IN MEGAHERTZ REFERRED TO LOWER
FREQUENCY LIMIT OF CHANNEL FIELD STENGTH AT POINT A SHALL NOT BE
GREATER THAN -20 dB
0.0A 0.5 1.0 1.25 2 3 4 5 6
5.755.45
0.75
MHz
MIN
3.579545
4.2 MHz
4.5 MHz
6.0 MHz
PICTURE
CARRIERCHROMINANCE
SUBCARRIER
FREQUENCY
SOUND CENTER
FREQUENCY
330
PHASE OF THE COLOR SIGNAL
REFERENCE
BURST
300
EI'
EI'
EQ'
EC'E
R'-E
Y' / 1.14
B'-EY' / 2.03
CHROMINANCE
SIGNAL
63
TYPICAL BROADCAST SYSTEMS
Every broadcast station is shaped by its market, economic forces, programming
type and style, environment, and many other factors. These factors result in each static
becoming a unique entity. It is very doubtful that a typical or average station can be
described with any degree of accuracy, but even though each station is unique, all
stations have many things in common. And one thing all do have in common is the need
for technical maintenance.
Because of this uniqueness of each station, the engineers charged with the
installation, maintenance and operation of a station must be able to shape general
principles into a form that apply at that particular station. And to apply the general
principles to that station, the engineer should have an understanding of its technical
system.
In the discussions that follows, some of the factors which go into the shaping of a
station are discussed briefly, and then a method is explained which help the engineer can
bring the technical operation of his station into better perspective.
The physical arrangement of the station and many operational factors dictate
some of the basic equipment requirements. These also contribute to the technical
complexity of the station and the maintenance problems.
COMBINED STUDIO-TRANSMITTER
This arrangement is popular at many stations but all can use it. All of the studio
and transmitting equipment is housed under one roof with the antenna nearby. The
control room, studios, and transmitter are all clustered together for case of operation.
The transmitter may be located in the control room itself, or in an adjacent room where it
can be observed through a soundproof window. This arrangement is the most efficient in
operation and requires the least amount of equipment. Also the job of maintenance and
making measurement is easier to perform.
There are at least two variations of the, combined studio-transmitter
arrangement. Although the studio and transmitter are combined under one roof, the
transmitter may be located in another room or on another floor. The transmitter is no
farther than 100 ft of more than a floor away from the operator. Whenever the
transmitter is moved away from the direct visual or manual access by the operator,
additional equipment is required and the system’s complexity increases. Maintenance
problems increase in direct proportion. The transmitter must have extension meters, and
there must be a wired control so the operator can monitor and operate the transmitter.
In the second variation, the transmitter may be over 100 ft. and several floors
away. Once the transmitter has been moved out past the limits described in the first
variation, the station requires special FCC authorization, and a regular remote control
unit must be used. Such arrangements are often found where tall buildings are
available. The transmitter is located on the top floor and the antenna on the roof of the
building. The building supplies tower height, and the use of a floor close to the tower will
reduce the length of transmission line needed.
SEPARATE STUDIO-TRANSMITTER SITES
This is a very common arrangement. The studios are located at some convenient
place of the city, while the transmitter and antenna may be several miles away, usually
out in the country. This is also the most complex of the arrangements and requires
considerably more equipment. Maintenance and measurements are more difficult to
perform, and travel time often becomes a factor. In those stations that do not have
operators on duty at the transmitter site, security of the building also becomes a factor.
Unmanned transmitters must have a FCC remote-control authorization and an approved
remote-control unit in operation.
The two sites must have an interconnection link. There must be an audio circuit,
a circuit for controlling functions of the transmitter, and provision for monitoring
transmitter parameters. The interconnection link is often provided by the telephone
company, but in may also be a station-owned microwave link.
Type of Services
AM and FM stations, while both engaged in broadcasting, operate in different
services. Everything at the transmitter and beyond is also different. So the service affects
the equipment required, and maintenance problems are also different. The audio
equipment can be the same for both types of stations, as long as the FM is a monaural
service.
64
Style of Operation
The “live” style of operation will dictate a certain a number of equipment times as
well as their arrangement. This type of operation is used by many stations. Typically, the
majority of programming comes from records played on turntables in the control room,
operated by a combo man (one who also acts as an announcer). In another live station,
there may be both an announcer and an engineer performing the work in two different
rooms-that is, an announcer’s booth and a central room working together. The combo
arrangement usually requires the least amount of equipment.
Stereo Operation
For FM stations that operates in stereo, the equipment requirement literally
double from those of monaural operation. And stereo places more exacting demands on
equipment performance and operating practices. This also creates numerous
maintenance problems. There must also be special stereo monitoring equipment and an
FCC approved stereo modulation monitor for the transmitter. And to convert the left and
right audio channels to a composite signal which modulates the transmitter, a stereo
generator is required.
At this time there are two additional proposals before the FCC, but as yet there
has been no approval. These are for quad stereo and AM stereo. The quad method uses
four channels instead of the present two. Quad is being transmitted now, but it is
converted to two-channels for transmission and then converted back to quad at the
receiver.
The proposal for stereo on AM is for two-channel system. The main carrier would
be amplitude modulated as is now done, and the sub channel would phase modulated the
carrier.
Antenna Systems
The antenna system of a station is often a very strong determining factor in how
the station is arranged and the equipment to be used. Besides the technical
requirements, there are often site problems. And when an AM station must use a multi-
tower, directional antenna system, the equipment, problems, and maintenance all
multiply rapidly.
The FM antenna must have relatively great height because of the transmission
characteristics at VHF. The antenna itself is relatively small, so it must have some tower
or other supporting structure for height. The antenna may be mounted on a short pole
above a tall building, or on its own tower mounted on the ground. In either case, a
transmission line is necessary to carry the RF from the transmitter to the antenna. Long
lines in not-too-accessible locations make it difficult to perform maintenance, and when
repairs are necessary, rigging equipment and tower must be called in to do the work..
While the tower is the supporting structure for the FM antenna, in AM the tower
itself is the antenna. Although many stations can operate with only a single tower, a
great many of them must use a multi-tower directional system. These systems require
several towers working together use a multi-tower to obtain the required radiation
pattern. Still other stations use two different directional patterns, one for day and the
other half is the ground system underneath the tower, made up of many copper wires
fanning out from the base of the tower at least as far from the tower as its height. These
can be simple two-tower arrays or multi-tower arrays. They all increase the station’s
complexity.
To demonstrate how various factors can shape the station into a unique individual
and affect its operation and complexity, one station with which I had a special and
problem required two different directional patterns for its day and night operations. It
wasn’t possible to create these two patterns from the same set of towers at this site.
Consequently, it had to erect an additional multi-tower antenna system at another site
11 miles away! There are two different transmitter sites, one for the day operation, and
one for the night operation. Fortunately, there are only a few stations with problems like
this.
Directional antennas take up a lot of real estate, which is one of the reasons that
most of them are located out in the country. There are many stations today that operate
with a directional system out in the country and the city grew out past them.
Peripherals
Peripheral operations abound at any station. These are programming activities
that cluster around the core of the station and make a heavy contribution to the station’s
programming. One important area is the news-gathering operations and the news room.
Newsrooms today are often very well equipped with many electronic items.
Not necessarily associated with news, but often used by the news department, are
the mobile remote pickup transmitters. Some stations have several of these units. The
65
remote pickup requires its own peculiar methods of maintenance, and it generates its
own problems as it also involves a somewhat different technology.
Additional program services-such as connection to a national, regional, or sports
network, and the stations own remote broadcasting arrangements-contribute to the
station’s complexity.
Automation Systems
Program automation systems, whether used on a part-time or full-time basis,
rapidly multiply the needed equipment units, and if the system operates in stereo
doubles its complexity and maintenance problems. When it passes through an
automation system, there is a need for recording booths for local production purposes.
How well these are equipped depends upon how much of the automated programming is
created at the station. In a station that uses full automated programming, there usually
isn’t control room as this term is used in the general sense. One of the production booths
must have some arrangement so that it can be place on the air as a substitute for the
automation system when the system fails.
Complexity and Maintenance
It should be very evident that whenever a station grows more complex for any
reason there is a direct growth in the number of equipment items in use. And along with
this growth in complexity and equipment numbers, there is a great number of equipment
failures. This because there are just more things that can go wrong. Consequently there
is a need for more and better maintenance.
System Division
Although the discussion in this book must, of necessity deal in generalities, the
engineer on the must always try to relate these general discussions to the particular
stations on the job must always try to relate these general discussions to the particular
station for which he is responsible. Even though one station may have the same
equipment lineup and may operate similarly to another, they will not necessarily have
the same problems. Always remember that each station is unique. Each of its own parts
has its own stresses, wear, and possible abuses. For example, one station may have an
operator who pounds on the keyboard as if it were a ancient typewriter. I goes without
saying that the latter station will soon have to replace keys on the keyboard.
So the engineer can develop a better understanding of his own station and its
operation, the overall system should be divided into many separate parts. This does not
mean that the equipment should be physically rearranged or even that the divisions need
be written down on paper. However, drawing the divisions out in simple block diagram
form could prove helpful, especially when new members are added to the staff but the
divisions should be essentially be done in the engineer’s mind.
The Master System
This is a term that can be applied to the station’s complete, overall electronic
operation, from its microphone inputs to its antenna outputs. Everything within this
system must interface properly and work together as a single unit to produce the
station’s signal. This master system is made up of many parts that all dovetail together.
And this master system can be divided into subsystems in a descending order of
importance to a master system.
Major Subsystems
The first division of the master system is the major subsystem. There can be
several major subsystems of equal importance. A major subsystem can be described as
an operational area in which a number of units work together to create a somewhat
independent product or activity. One example would be the studio are of a station. All of
its various subsystems work together to create the station’s audio. This product is
generally used to modulate the transmitter, but it can also be used for other purposes. It
could, for example, be fed to a tape recorder. The recorded program could be sent to
other stations or reserved for use at another time.
This same thing can be applied in division of the master system into other major
subsystems according tot eh particular station arrangement. But do not have divisions
into major subsystems, than the particular situation warrants
Minor Subsystems
Each major subsystem can then be divided into minor subsystems, and again,
each of these ranked according to the importance of its role within that major subsystem.
And each minor subsystem can be further divided into its own subdivisions. This dividing
and subdividing creates a pyramid structure, all narrowing from a broad base to the
single master system at the apex.
Many individual items that are low ranked in this particular arrangement are very
expensive, high quality units that can stand as master systems in their own right-but in
other situations. A tape recorder, for example, is a complete unit in itself and can stand
66
alone. But when used in the control room as a program source, it plays a lesser role and
therefore is ranked as a minor subsystem. Thus, use in the operation determines the
ranking.
Maintenance Aids
Dividing the station into its various parts proves very helpful to an engineer when
problems develop and must be corrected in a hurry. It also helps the engineer visualize
the total operation and not become confused by an apparent variety of independent
operations. When he understands the total operation, he can quick ly isolate problems to
specific subsystems. Then another minor subsystem may be substituted, or bypass
arrangements can be made so the station can continue its programming with little
interruption.
Common Divisions
As was pointed out earlier, each station is unique, but all have many things in
common. In this chapter, we use the division method and discuss some of the equipment
found in the various subsystems of a station. In later chapter, those various equipments
are discussed in more detail.
Any station’s master system can be subdivided into at least three or four major
subsystems. In this chapter, we use the division method and discuss some of the
equipments in the various subsystems of a station. In later chapters, those various
equipments are discussed in more detail.
Any station’s system can be subdivided into at least three or four major
subsystems. Some stations may have more, but all will have at least this many. These
major subdivision are: studio area, connecting link, transmitter area, and antenna
system.
The Studio Area
This major subsystem is composed of a variety of minor subsystems, surrounded
by many peripheral subsystems, all working to produce the station’s programming.
Further subdivision can be made in this manner: control room and its minor subsystems;
recording booth and its subsystems; second; recording booth (if used); audio processors
(if used t this location); peripheral systems, starting with the newsroom and its
subsystems; remote pickup base transmitter and mobile units; network connection,
regional network, and sports network; local remote lines and QKT circuits (voice
coupler); and EBS (emergency broadcast system) equipment.
This is only a rough division, and each stations its own order of priorities
according to the actual equipment it has in use.
Control Room
This should be the highest ranking subsystem in the studio area of any station
that uses a control room. (Automated stations may not). In the control room, the highest
ranking equipment item should be the control console. All other subunits feed into this
console; there the programming material is mixed, blended, and controlled in the desired
manner to produce the finished program product. The console is often referred to as the
control board, or simple board.
Microphone System
Microphones originate a considerable amount of programming, whether live or
recorded. For the live-tape operations, in which the main announcers work out of the
control room, the microphones rank as a minor subsystem. There may be one or two
located in the control room, one or two located in an announcing booth, and one or more
located in each studio that is in operation. All of these feed directly to the console and
are controlled by it. Microphones are low-level devices, so they must have pre-
amplification. The preamplifiers are generally located in the console itself although in
some cases they are located in a rack.
Turntables
The second major source of programming is the turntables. There are a minimum
of two turntables in the control room. It is extremely clumsy for a disc jockey to do a
music show with only one turntable.
Although the term turntable is often applied to this program source, it is really a
system made of several subsystems: the turntable itself, drive meter, cabinet, cartridge
and stylus, tone arm, equalizer, and preamplifier.
The signal output of the pickup cartridge is a low-level signal that requires
amplification. The usual practice is to locate the preamplifier and equalizer in the
turntable cabinet itself, close to the turn arm. The equalizer may be a separate unit, or it
may be built into the preamplifier. The preamplifier brings the low-level signal of the
cartridge up to the program level of + 6 dB (decibel) or the level desired.
67
Tape Recorders
Another important program source for the console is the tape machine in the
control room. Tape machines may be of the open-reel type or the cartridge type. The
cassette recorder is another type that is increasingly common.
In most cases, the open-reel machine is basically two-system machine. That is it
is both a recording machine and a playback machine. It is the playback section of the
machine that is used as a program source for the console. It may play tapes that have
been recorded on this machine, other machines, or tapes that have been sent to the
station. The playback amplifier can provide normal + 8 db program output level.
The recorder section of the machine also has use in the control room. The input to
the recorder is often a selector switch so that the recorder can record from many
sources.
Cartridge tape machines are newer than the open-reel machines, and all stations
have two or more of these machines in use today. Besides the different method of
handling the tape, the configuration of these machines is often different. That is, many
are playback-only machines which can play only prerecorded tapes. And there are often
multideck machines that incorporate more than one playback section in the same unit. In
the multiple units, some of the functions are shared, such as the cabinet, drive meter,
etc. Ordinarily, each has its own head, playback amplifiers and control circuit. When
multideck units are employed, each slot is often referred to as a tray. For example, a
machine may be a 3-tray unit or a 4-tray unit. The output of each of these trays or each
unit is normally at program level of + 8 dB.
A cartridge tape system is somewhat limited if only playback machines are use.
So there is one or more recording units in the station, although the control room may
have only one.
Peripherals
As mentioned earlier, there are usually many peripherals in the studio area. They
vary from station to station, not only in type, but in numbers. Most stations have a
newsroom. And how large this area depends how much the station does in the news
area. A major newsroom has a small console or mixing arrangement along with open reel
and cartridge tape recorders. There’s a variety of electronic sources used in the station.
Most of these sources are channeled through the small console or mixer, so that editing
can be done and completed news tapes produced. In many stations, the news room is
well equipped so that it acts as a subsidiary control room for the news programming.
That is, when it comes time for the news., the newsroom is switched into the main
control room as though it were a remote control program, and the news is presented
from the news room itself.
There are many other items that are helpful in the new-gathering process, such as
receivers that monitor police, sheriff, and fire channels. There also may be a base
transmitter-receiver located here for use of the remote pickup mobile units for news
stories.
Remotes
Many program sources originate outside the station and are brought into the
station over telephone circuits, or there may be remote pickup stations. Each of these is
fed into the console in the control room for the switching, blending, and other processing
needed. Programs may originate at stores, auto showrooms, fairgrounds, or any place
that makes a good program or news source. These wire circuit are called broadcast loops
and are leased from the telephone company for the occasion. Some may be equalized,
others not, depending upon the quality of circuit required.
QKT Circuit
This type of circuit has become popular in recent years because it can be less
expensive on a long-distance than regular broadcast loops. The QKT, also called voice
coupler, is supported by the telephone company. It is a regular telephone that contains
either an exclusion key, or a cutoff key, and a transformer to connect the stations remote
amplifier to the telephone circuit. The broadcast are handled as regular long-distance
telephone calls. At the studio, it is necessary to arrange a connection to the telephone
circuit for the phone number in use, that is, a connection to th console.
Signal Processing
There may be several processors in the studio area. These are devices such as
AGC amplifiers, peak amplifiers, peak limiters, etc. They may be used at any place this
action is required. In separated operations, they may be placed at either or both ends of
the connecting link.
68
Processors are also used with production booths, and AGC amplifiers are often
used to control incoming levels from a remote line. Here again, the use and location of
the processor determines its ranking in your divisions.
Other Program Sources
There may be a variety of program sources feeding the console besides the
equipment in the control room. Each station apply a ranking to the source according to
its importance to the station. That is, if the station carried a very heavy schedule from a
sports network, this network is given a higher ranking than an occasional remote. Other
sources can be from a sister AM, FM, or TV station, the newsroom, or a production booth
acting as a subsidiary control room.
EBS Equipment
All stations are required to have a receiver that receives the EBS alerts from key
stations, and they must also send out EBS tests each week. The new FCC rules, which
went into effect April 15, 1976, requires that a dual-tone system is used. That is, two
tones-853 Hz and 960 Hz-are transmitted for 22 seconds. The receiver must be in
operation all the time the station is on air and must set off alarms when the alerting
signal is received. There have been many changes in this system since origination.
The Connecting Link
The second major subsystem that some stations have is the connecting link
between the studio and transmitter. For stations with the transmitter in the control room,
or in the next room, the connecting link is simply a pair of audio cables. A simple
arrangement like that is hardly considered a major subsystem. But many stations have
their transmitter out of sight and out of reach of the operator. The connecting link then
does become a major subsystem.
Whenever the transmitter is far away from the operator, he must be able to
monitor and control it, as well as feed the audio signal to the transmitter for modulation.
There must always an audio feed from the audio to the transmitter from the program
audio. So let’s consider the first.
Audio Circuit
The audio circuit is perhaps the most important subsystem of the link. The quality
of this circuit must be at least as good as that required of the rest of the station itself.
The audio-frequency response, distortion, and noise are the basic characteristics.
Although line losses are also a factor. A simple way to remember the quality of line
needed is to consider the limits allowed when making a proof of performance. All the
system audio must pass through this circuit. These are usually telephone lines that
equalized. And if the station transmits stereo, two identical circuits are needed for the
left and right audio channels.
Transmitter Control
The operator must be able to do everything (almost) to the transmitter at a
remote location that he can do while standing in front it-at least the controlling functions
of turning it on and off, raising power etc. This involves a remote-control system. There
are different models of remote-control units, and some of these use metallic telephone
circuits. There is a sending unit at the studio which controls the different functions of the
transmitter through a receiver unit at the transmitter site.
Metering
All of the important parameters of the transmitter must be metered. The
parameter samples are sent from the unit at the transmitter site to a receiving unit at
the control point, where they operate one or more meters. These devices usually scan
the samples in sequence, and the unit at the control point is synchronized to this scan. In
the sample units, these are stepping relays that send DC (direct current) voltage samples
to be measured. A single pair of wires is needed.
Sophisticated Units
Besides the simple control units, there are many modern, sophisticated units.
These are basically digital devices that convert analog samples and control functions to
digital signals. These are (frequency-shift keying) of an audio carrier signal to transmit
information over the lines, if the telephone company pairs, or the modulator of an STL
(studio-transmitter link) microwave unit owned by the station.
STL
As just mentioned, these are microwave links. Such links are common in
television stations and are becoming more common for FM radio. They are not as yet
very popular in AM broadcasting. When the station uses its own microwave link, except
for the quirks of Mother Nature on propagation, it places the control of the connecting
link back in the station hands. The STL, by the way, only replaces the telephone circuits
that would otherwise be used. There must still be a remote-controlled unit for the
transmitter.
69
Monitoring
Transmitter parameters must be monitored-also the antenna system, tower lights,
and building security systems (if used).
Transmitter modulation must be monitored by an approved modulation monitor.
When the station is operating by remote control, the modulation monitor must be located
at the remote-control point. When placed at the remote-control point, an RF amplifier is
often required to increase the RF signal level that the monitor can operate properly.
When work must be done at the transmitter site that requires a monitor, there can be
some extra difficulty in doing the maintenance.
Controlling and monitoring the transmitter from any distance can become a rather
complex operation (Fig. 1-10). When the more sophisticated remote-control units are
employed, and a STL, then other technologies become involved; digital and microwave.
When dividing by the subsystem method, the rank must be established according to that
which is used at a station. Several of these technologies can be of equal rank. But always
remember that the ranking is relative; it is designed to help an engineer quickly isolate
problems that develop, as well as aid his understanding of the overall station operation.
Transmitter Area
This the third major subsystem of the master system. This equipment receives the
audio from the studio area, develop the RF carrier, impresses the audio on the carrier
modulation, and sends it to the antenna system for radiation. This area includes systems
that could be classed as major systems, but in a station they work together as part of
one major subsystem.
Transmitting Gear
Any transmitter is composed of many internal subsystems. Transmitters differ
according to make, model, power, range, and type of modulation. The transmitter usually
a self-contained unit that requires only an audio input and AC power input to provide a
modulated RF output to the transmission line.
AC Power Input
Low power units work on 230 V AC, single phase, while the high-power
transmitter employ three-phase 230 V AC. Very high units use 440 AC, this AC power is
brought to the building over high-voltage mains, then stepped down to the 230V by the
transformers on a pole or on the ground. It is fed to main power entrance, where there is
fuse protection. Then it is distributed through out the building. One of these circuits feeds
the transmitter. In some of the older transmitters (and even some newer ones), the
transmitter crystal is installed in an oven; this even usually has a separate AC circuit. The
power feed should be through conduit.
Audio Input
The audio from the control room must be fed to the transmitter audio input. This
audio is usually run through processors before it gets to the transmitter itself. This
usually is an AGC amplifier to control program levels and a peak limiter right before the
transmitter. There may also be speech enhancers or other dynamic equalizers in the line
also. The Ac and limiting amplifiers may combined in a single unit or may be separate
unit. When the transmitter is at a distance, these processors may be split up, or they
may all be at the transmitter site. Much depends upon individual preferences and the
particular situation. There are different types of processors used for FM and AM, as well
as a different arrangement when stereo is in use. The same types can be used, but today
the ordinary AGC amplifiers and peak limiters are giving way to more sophisticated
types.
Peak limiters, designed for AM, switch the highest peak of a cycle to the positive
modulation side before sending in into the transmitter. This allows the positive
modulation to the higher than 100 % and at the same time limit the negative side to no
more than 99 % modulation. The output of these units is polarized.
FM peak limiters must contend with the 75 microsecond pre-emphasis in the
transmitter. So some shape the audio to a true pre-emphasis curve by clipping, if need
be, so as to attain a higher degree of modulation without over-modulating. Both stereo
AGC amplifiers and limiters are strapped together so that they operate as a single unit,
although controlling both left and right audio channels.
Stereo Generator
With stereo, the audio signals must be processed through a stereo generator
before they are fed to the transmitter input. The generator is a very important subsystem
in the stereo process. The composite output of the generator modulates the transmitters-
not the audio signals themselves. The generator output contains both audio and super
sonic signals that have been specially processed.
70
The monitoring of the transmitter can be classified in two categories: the
modulation and the parameters.
Modulation- There must be an FCC- approved modulation monitor in operation. The AM
monitor has provision for monitoring the positive or negative modulation envelopes,
provides audio output for speaker monitoring (after amplification), and provides the
output for measuring audio distortion during proof-of-performance measurements. The
FM monitor provides the same capabilities as the AM monitor, except that the positive
and negative modulation is not as important. The FM station does not use asymmetrical
modulation as do many AM stations. If the FM is stereo, there must be an FCC-approved
stereo monitor. This monitor has many additional capabilities and provides many
switching positions and pads for making the stereo proof measurements.
All monitors will have provisions for remote metering of its various functions
necessary for the FCC-required monitoring of percentage of modulation. These function
can be routed over an extension-metering arrangement.
Parameters- Certain parameters of the transmitter must be metered and legged. When
on remote control, or if extension meters are used, a sample of the parameter must be
provided. Most modern transmitters already have the samplers built into them. Older
transmitters, however, may not have the samplers, and these must be added. The
output-stage power input-that is, voltage and current-and the transmitter power output
must be logged. There may be other samplers provided also.
Transmission Lines
Once the RF signal has been generated and modulated, it is sent to the antenna
over transmission lines. Some stations still use the old open-wire transmission line, but
the majority use coaxial line. Coaxial lines come in different diameters, are either rigid or
flexible, foam filled or air dielectric, and may bare on the outside or jacketed. Air systems
may use dry air or gas under pressure. Pressurization may be done by gas cylinder or an
air pump.
The length of the line between the transmitter and tower is called the horizontal
run. This may be suspended on posts or buried under ground. When the line feeds an FM
must also continue up the tower. This is called the vertical run.
When a transmission line is not properly terminated, standing waves are sent up
along the line. That is, some of the transmitter power is reflected back to the transmitter.
The standing–wave ratio (SWR) is the ratio between the forward and reflected powers. If
the voltage of the waves is used in the calculations, the term is VSWR.
Standing waves on the line can cause damage to the line itself or to the output
stage of the transmitter. FM transmitters use a device that monitors this VSWR and shuts
the transmitter off when VSWR reaches a predetermined value.
Cooling Systems
Transmitters must have cooling for proper operation. There is a subsystem built
into the transmitter to provide its cooling. The air or water temperatures in the cooling
system are sampled, and if the flow stops or decreases, an interlock shuts the
transmitter down.
Transmitters are also designed to function within certain ambient temperature
ranges that are operating temperatures. Either end of this range may be uncomfortable
for humans. But if the ranges of air temperatures vary outside the transmitter limits,
cooling or heating must be added.
Antennas
The antenna system is the final point where the station has control over its signal.
The antenna system is complex enough to be classed as a major subsystem; this is
particularly true of the multitower AM directional systems. AM and FM antennas are
classed in different categories. Their treatment is different because of the difference in
frequencies. They require different operating and maintenance practices.
AM Antenna
This may be a single tower, or many towers in an array. The tower itself is the
antenna, so its height has a definite relationship to the station’s carrier frequency. Thus a
vertical antenna is used, with the other half of the antenna system in its ground system.
Primary coverage in AM broadcasting relies on the ground wave signals. The ground
waves do enter the picture, and that is the reason stations cut back power at sunset and
change to directional patterns, for the sky wave reaches farther after sunset.
71
Antenna towers may be either self-supporting or guyed. When guys are used,
they are segmented with insulators so the guys do not affect the radiation of the signal.
The guys are not part of the antenna; they are only for support.
The antennas may be series fed or shunt fed. There are some shunt-fed towers
around today, but the majorities are series fed. In this method, the antenna must be
insulated from ground.
Coupling Units
When a series-fed antenna is used, a coupling must be used to match the
transmission line to the antenna. This unit is usually a T-arrangement of coils and
capacitors which matches the impedance transmission line to the tower, canceling outr
any reactance of the tower itself.
In the directional system, each tower has a coupling unit, but there are also
power dividers and phasers that divide and distribute the RF to the different towers in the
array in the amounts needed to obtain the desired pattern. The whole system is
interconnected with coaxial transmission lines.
Antenna Monitoring
In the single-tower, omni-directional system, the power at the base of the
antenna must be measured as the station output power. In a directional system, the
power to the common-point feed of the system is measured for power output. And the
phases and base current of each tower must be sampled and fed back to a phase monitor
so that the proper operation of the antenna can be observed as an operational
requirement. The samplers for this are usually small loops mounted at the appropriate
place on each tower, or on poles away from the tower, yet close enough to get an
adequate sample. The RF samples are fed back to the transmitter room over small-
diameter coaxial lines.
FM Antennas
This antenna is small in physical size because of the carrier frequencies (VHF)
used. Because of the small size, many antennas are often stacked one above the other,
suitably spaced. This arrangement provides power gain. Each one of the units is called a
bay; the whole array is in the antenna. A directional pattern is possible when antennas
are stacked, but the usual pattern is circular (but with increased power gain). Although
each bay may be small, a typical 12-bay antenna can measure 100 feet in length.
FM propagation-signals at VHF behave far differently than those in the AM
broadcast band. They tend to travel more in the line of sight, although they do get far
over the horizon. They suffer more propagation losses. To overcome some of these
factors, the antennas are mounted as high as possible within the limitation set by the
FCC. This ordinarily requires a tall steel tower, unless a suitable building or other tall
structure is available.
Weather Effects on FM Antennas-Weather affects the FM antenna far more than it
wills the AM antenna. Heating and cooling by the air or sun can cause the elements to
expand or contract and detune the antenna. The most serious problems is sleet or ice
forming on the antenna. This will seriously detune the antenna and cause serious VSWR
losses on the transmission line. To overcome this problem, heaters are inserted in the
antenna elements to melt any sleet or ice. These heaters are operated from 120V or
230V AC and are usually thermostatically controlled by a unit mounted near the base of
the antenna. In some areas of the country, where icing is a very severe problem, the
entire antenna is often enclosed in a random.
Towers
Towers are used as supporting structures for FM antennas or as the antenna for
AM stations or a tower may serve in both capacities at the same time. Aside from the
electrical characteristics and considerations as antennas, towers are large physical
structures that require maintenance if they are to remain standing for many years.
Both for greater visibility and weather protection, the towers are painted. This
painting and the colors used must conform to the FCC rules. The painting is mainly for
visibility, but id does add increased weather protection. Other methods, such as
galvanizing, will contribute the major share of weather protection. Weather is not the
only thing the metal must be protected from, for there are other chemical elements, such
as salt near the oceans and a variety of chemical elements added to the air industrial
areas.
Also for visibility, the tower must be lighted, and the lighting arrangement must
conform to FCC standard. The rules specify a different arrangement for different to
heights, depending on whether the location is close to an airport or air lane. The lighting
system requires 120 V AC, and there must be one flashing beacons and aid marker lights
at different levels. These lights must be turned on at certain levels of sky intensity
72
Control Room
Transmitter
Combined Studio Transmitter Arrangement. This is the simplest form and requires
the least equipment
(light), which is usually sensed by a photocell. This lighting must be observed each day
for operation and then logged. If the tower cannot be visually observed, then samplers
must be included that send data back to the control point to indicate that all lamps are
operating properly. A new method of lighting recently developed is high-intensity strobe
lighting. This type can be seen farther than conventional lamps.
Lightning Protection-Of course, a tall tower makes a likely target for lightning. Lightning
develops tremendous forces, and the best we can do is diverting it to prevent damage.
Unless some precautions are taken, damage can result the elements in the tuning
section, transmission line, transmitter, and transmitter buildings. Some very complex
arrangements have been developed to prevent lightning strikes. Old-time remedies make
use of lightning rods on the tower, ball gaps across the insulator of an AM tower, and
static-drain chokes.
Isolation-The AM tower must be insulated form ground. But there are many metallic
conductors that need to cross the base-so special arrangements must be made.
Tower lightning and heaters for FM antennas require 120 V AC. There are two
ways to cross the base with AC power. The first is the large open-ring transformer. There
is no connection except through the magnetic flux of the transformer windings. The
second method feeds the AC power through large RF chokes.
FM antennas may be mounted at the top of an AM tower. The coax transmission
line must cross the insulator at the tower base. Again, there are two methods of doing
this. The preferable way is through an isolation unit. There is no direct connection to this
unit. It maintains the impedance characteristic of the coax line. The quarter-wave length
is figured at the FM carrier frequency.
When directional AM antennas are in use, the RF signals from the samplers are
fed back over small coaxial lines. These must cross the base. Usually, large coils of the
line are formed in an amount that creates an RF choke at the AM frequency to prevent
shorting out the base. In another arrangement, the sample loops are on small wooden
poles on the ground, but close enough to get an adequate sample from the tower.
73
Station Building
Control
RoomStudio News Transmitter
not over 100 ft. away
1st floor
tall building
roof
transmitter
2nd
Two variations of the combined studio-transmitter arrangement. The transmitter is not over 100 ft
away nor more than one floor away. In the lower figure, we have the second variation, in a tall
building. This requires NTC remote control authorization.
74
air
lights
mike(s)
tt's
cart. tape
news room
reel tape
sports
net etc.
inputs
(ranked acording to importance)
ac power monitors muting
outputsinputs
(rank 2) (rank 1) (rank 3)
(rank 1)
control room
program bus
console
Typical minor subsystem of the studio area. This is similar to a regular block diagram, except placement
should be according to importance of role.
Note 1. Meters must be calibrated each week
2. There is more difficulty making measurements
Moving the transmitter out of direct visual view and control by theoperator increases station
complexity and requires more circuitry and routines. Above, the simple system requires nothing
more than a pair of audio wires. Below, there must also be wire control circuits and extension
meters. The further away the transmitter is moved, the more complex it becomes
control room transmitter
pair of audio wires
less than 100 ft.
audio pair
direct wire control circuits
extension meters
control room transmitter
75
11 miles apart
directional
antenna for
daytime
pattern
site 2
site 1
transmitter
transmitter 2
studios
directional
antenna for
nighttime
pattern
MIN
SMIN
S
MIN
S
MINOR
SUB-SYS
MIN
SMIN
S
MIN
S
MINOR
SUB-SYS
ETC.ETC. ETC.
MAJOR
SUB-SYS
MAJOR
SUB-SYS
MAJOR
SUB-SYS
MAJOR
SUB-SYS
MASTER
SYSTEM
Basic outline of the master system division into subsystem. This is similar to a
company's personnel organization chart. Subsystems at the low end of the stack
play the least role in station's system.
Studio
Area
Connecting
Link
Transmitter
Area
Antenna
Systems
(activity flow from left to right)
The most common division of any station into four major subsystems
76
Tower and Antenna
The final control a station has over its signal is at the antenna. A good antenna
system is required so that the RF signal can be radiated in the most efficient manner.
Antennas for AM and FM are physically different because of the carrier frequencies and
propagation characteristics. They must also have somewhat different operating and
maintenance techniques.
The AM Antenna
Wavelengths in the AM band are rather long and require physically long antennas.
One full wavelength in the middle of the AM band at 1000 kHz, for example, is 984 feet.
This would require an antenna almost as long if full-wave antennas were used.
Propagation of the signal is by both the sky wave and ground wave. The ground
wave is more reliable for local coverage, while the sky wave is best for long-distance
communications. In broadcasting, the sky wave is undesirable, as it causes interference
to stations on the same channel located many miles from the local station. The
wavelength of the antenna that is used affects the direction of radiation of this sky wave,
so a length is chosen that will reduce the sky wave as much as possible.
The Other Half
The antenna is actually made up of the antenna itself and its ground system. The
ground system may be buried in the ground beneath a tower out in a field, or a counter-
poise arrangement if located on top of a building. The ground system should always be
considered as half of the antenna for maintenance and installation purposes. That is, half
of the antenna is in the air, the other half under ground. This is somewhat analogous to a
half-wave dipole stuck in the ground. Actually, it is only a loose analogy, for either the
actual shape or size approaches that of the dipole; but it does help illustrate the ground
system as an important part of the antenna.
The ground system is not used in the sense that other grounds in the station are
used. In those applications, we want to tie a shield or component to a zero-voltage
reference point. At the antenna, however, we tie the tuning coils and coax outer
conductor to the other half of the antenna. If you will visualize the antenna and ground
system in this manner, then you will be apt to take as much care in making connections
to the ground system as you do the antenna proper.
Electrical Values
The tower is insulated from ground, and its length is some part of a wavelength at
the carrier frequency. It will exhibit RF resistance and reactance, depending upon this
relationship. Besides the height, the actual physical shape of the structure, as well as
large objects nearby, will affect these values. This is an important fact to remember
when considering erecting another tower or some large metal object nearby.
Aside from the ability to tune or resonate the tower in use, power-consuming
factor such as high resistance joints can enter the picture, reducing the actual radiating
efficiency of the antenna. So when making connections to the tower or ground system,
remember to keep these as low in resistance as possible.
Tuning Unit
The RF power from the transmitter will be fed to the tower over a transmission
line. When coax is used (as in most cases), the line exhibits its own characteristics and
“temperament” when not terminated properly. To obtain the most efficient transfer of
power through the line, the line must be terminated in its natural impedance and zero
reactance.
It would be a rare case indeed to find an antenna that would exactly match the
line directly. Consequently, a tuning unit is used to match the two together. This unit will
usually contain a T-network made up of series and shunt coils and capacitors. Besides
matching the impedance of the line and the antenna resistance, the circuit will also
resonate the tower and act as a filter to attenuate any harmonics of the carrier that
might be present.
Bandpass
Antennas are usually tuned to obtain the greatest efficiency in radiation. Tuning
for the greatest efficiency, while it will produce a higher radiated RF signal, will also
increase the Q of this system. High-Q systems become narrowband, so sideband clipping
will take place. This will limit the station’s bandwidth.
The AM station is permitted an occupied bandwidth of 30 kHz. This means that
theoretically, the transmitter can be modulated out of 15 kHz audio. In practice,
however, most of the older rings will not pass this high an audio frequency. The new
transmitters, however, can pass well over 10 kHz.
77
To obtain the greatest fidelity, the antenna system should be broad banded.
Included in the broad banding are the harmonic filters and tuning coils at the output of
the transmitter proper. The match at the tuning unit should also match the coax line
impedance across the band pass, or there will be a high VSWR at the unmatched areas of
the band pass. These can introduce distortion. Lack of broad banding limits the static
potential fidelity.
Larger System
The antenna and its ground system are often a part of a larger antenna system.
Many stations use directional antennas all or part of the time. While each tower in the
system must perform its own role, the very close proximity of the tower, whether they be
a fault or a deliberate change, it will affect the entire system and the radiated pattern.
This is something to bear in mind when making repairs to a directional antenna system.
Installation
Station personnel do not erect tower, but they will very often install the ground
system. The design of the ground system will be spelled out in the construction permit,
so it must conform to this.
The installation should be done in a careful manner. If done in a haphazard
manner, it is possible the finished job will end up with irregularly spaced radials, or worst
not enough. Before starting, plot out the installation and stake it out. The best way is
with a surveyor’s transit. If this is not available or you don’t know how to do one, then it
can be done in another way.
First, compute the length of the chord between the two terminating points on the
circumference of the circle described by the radials. Measure off a length of ground wire
this length or use a tape measure. Next, measure off one length of wire for a radial. Take
the end of this radial straight out from the tower until it is taut. Drive a stake into the
ground. Now either use a tape measure or the other length of wire you measured and
anchor this to the stake. Take the free end of the radial wire and move to a point where
both wires are taut. This is where the next radial belongs, so drive a stake in there.
Continue this process until all the radials are plotted out.
Plow It In
The ground wires must not be left on top of the ground, but must be plowed into
the soil about six to eight inches. Either construct a simple plow arrangement or use one
of the commercial wire plows to do the job. All that is needed is a thin slit in the ground
and something that will insert the wire in the bottom of the slit as the plowing is done.
Plow a straight line, and on the return trip, run the tractor wheel over the slit to
close it back up. Make sure the end of the radial is buried and remove the stake. There is
no point in advertising where the end of the radial is buried and removes the stake.
There is no point in advertising where the ends of the wires are. If the stakes are left in
or the wire ends sticking out, this is an invitation to thieves or vandals to pull out the
ground system.
Connections
All the radials and the copper screen below the tower will have RF currents in
them. the currents at the base of the tower will be high (Just as they are at the base of
the antenna proper). Wherever two wires cross or touch each other or the copper screen,
make a good mechanical and solder connection. On the screen, make these at least
every two feet. Intermittent or corrosive connections can use arcing noise in the program
or introduce an inter-modulation component.
The ground system will down for a good many years, so use a hard solder, such
as silver solder. This is more difficult to work with, but it makes a stronger connection. If
there is a wind, arrange some type of shield, or the wind will slow up the process. Use
torch with a narrow flame for best and quicker results.
Tuning Unit
Take as much care with the connections to the ground system here as you do to
the antenna proper. Use heavy copper strap and hard solder. And when attaching to the
tuning-unit box, make sure the point is cleared off to get a good metal contact. Some
boxes have a second inner chassis. Make sure the chassis and the outer box are securely
bonded together and to the ground system. If there is a poor or loose connection here,
the antenna system will become erratic, or unstable. This is because half of the system is
“floating” because of the intermittent ground connection.
FM Antennas
The radiating elements of the FM antenna are much smaller than those in the AM
system; the wavelengths are much smaller. For example, at 100 MHz, in mid-band, a full
wavelength is 9.84 feet, contrasted with 984 feet of the AM band.
78
Propagation characteristics are also different, in that the FM signal tends to travel
in a straight line horizontally from the antenna. The FM antenna is required to be
horizontally polarized, whereas the AM antenna is vertically polarized. Other polarizations
may be added to the horizontal polarization, but FCC approval is needed.
Power Problems
Each FM antenna is a dipole that is either formed into a circle, or into a V-shape.
These are the basic shapes, but a vertical element may be added, or the elements may
be bent into an oval shape. These additional shaping are used when additional
polarization is added.
Each basic dipole has a gain of approximately 1. When vertical polarizations are
added, the gain is reduced to 0.5 in each of the polarizations. The total gain for the
antenna is still 1, but it will divide the power pair into two separate fields, the horizontal
and vertical fields.
The receiving antenna will usually only receive one or the other field, dependent
upon its polarization. So the voltage in each field is now less.
You don’t get something for nothing. If you want to divide the power into two
fields, then you must double the input power tot eh antenna to recover the original
radiated power in one field. Of course, some vertical polarization is most desirable
because it provides a better signal to automobile FM radios.
Stacking
The small physical size of each FM antenna lends itself to stacking. When
individual units (called bays) are stacked each will contribute its gain figure to the total
gain. Typical high-gain antennas of 12 bays are often used, and this will produce a power
gain of approximately 12. Thus, if 1 W was fed to the antenna, it would radiate 12 kW.
This is called ERP or effective radiated power.
Stacking has its penalties also. The beam is narrower, and it can become highly
directional just like a multi-tower AM system. Directional FM antennas are not used
(except in special instances), rather an omni-directional antenna is desired.
Careful phasing of the individual elements produces an omni-directional pattern.
The narrow bandwidth can produce holes in the close-in coverage area. Again special
phasing is done to reduce this effect. Twelve bays seem to be about the practical limit for
stacking, as the entire unit can become very long. A 12-bay unit for some FM channels
can be well over 100 feet in length.
Pattern Distortion
Although all the bays are carefully phased to produce an omni-directional pattern,
this will hold if the antenna is mounted on a very slim pole mounted above the tower.
But a great many FM antennas are side-mounted on a tower. The proximity of the tower
will affect this pattern considerably. So when an antenna is to be side-mounted, then the
manufacturer must have the dimensions of the tower structure so that appropriate
compensations can be made to the final tuning to produce the desired pattern.
Remember that these are still only theoretical calculations, and when the actual
mounting is made on your tower, there can still be some distortion of the circular
pattern.
Matching
The antenna is fed by antenna coaxial line, so the antenna must present a purely
resistive, zero reactance load to the line. The tuning unit for this purpose is a coaxial
transformer, which will mount at the base of the antenna feed point. Then are covered
openings that can be taken off, and shorting or tuning slugs that can be moved to trim
up the impedance match. Once the tuning has been accomplished, the covers are
replaced and the line made gas tight so that the whole system can be gassed if desired.
Installation
The antenna is assembled at the factory and tuned up on the station’s channel.
Then it will be disassembled and shipped. During this process, it is possible some of the
elements will be damaged or lost. So look all the components when they arrive. If tuned
elements are bent, it will affect overall tuning the pattern of the antenna.
Where the bays were originally installed, there should be a mark of some kind. It
is important that they are put back together, not only in their original line up, but so that
one or more bays are not turned over. This reversal would reverse the phase of the bay
by 180 degrees. Any of these situations will affect the pattern, impedance match, and
operating parameters of the antenna. So put it back together carefully. Now you won’t be
up the tower installing the antenna, but make certain the erection crew understands the
importance of all these factors.
79
Alignment
Not only must all the parts of the antenna be put back together properly, they
must be lined up perfectly in the vertical position, and the aperture at the face of the
array should be straight (gap between the ends of the horizontal elements). If the whole
antenna tilts forward or backward mechanical beam tilt is introduced, and this is not
permitted unless the construction permit specifically allows a definite amount.
Before everything is finally bolted tightly into place, use a surveyor’s transit and
view the antenna from the side. You should be able to tilt the transit from the top to
bottom of the antenna and find every bay on the same position of the crosshairs. Then
go to the front of the antenna. Again, you should be able to tilt the transit top to bottom
and find the gap at each bay on the same position on the transit top to bottom and find
the gap at each on the same position on the transit’s crosshairs. When this is the case,
lock everything in place.
Transmission Line
The coax line will run on up the tower to the antenna matching unit. If this is a
flexible line, band it to the tower leg every two feet. A rigid line must use hangers every
ten feet. If the coax line has an outer insulating covering, then peel this off at several
places and bond the copper outer conductor to the tower. If that tower is an AM antenna,
the bare line must be connected tightly to the tower to prevent arcing, and if the line is
insulated, then the outer conductor must be connected to the tower to break up its
length relationship with the AM carrier.
Isolation
When the tower is an insulated AM tower, another problem presents itself. The
coaxial line must be isolated or it will short out the AM antenna. This same holds true for
any metallic conductors that cross the base, whether it is AC power or coax cable to a
remote pickup antenna, or coax to sampling loops. These must be RF insulated, not
simply DC insulated. The fact that there may be an insulated, not simply DC insulated.
The fact that there may be an insulated covering on the cable will not prevent it from
shorting out the AM tower. There are at least two methods used to insulate the FM
coaxial line.
Coupler Isolation
An isolation unit. It is a metal box that is gas tight and completely insulated at its
input and output. That is, both the inner and outer conductors of the transmission line
are insulated. There is a loop coupling to the two sides of the circuit. By special design,
the line impedance is not altered, so that the VSWR with the unit in the line is very small.
Since there will also be RF voltage stress from the AM carrier across the unit, it is rated
for different levels of AM carrier power as well as the FM power.
There are mechanical stresses as well as RF stresses on the unit. Pressure from
the line expansion and contraction can break the insulation and allow a gas leak. And the
RF carrier from the AM can melt the ceramic insulators. If the line is un-gassed and a
leak occurs, moisture can get in and rust the box.
Bazooka
This is a tuned line section and makes use of the high impedance of a quarter-
wave line section that is shorted at one end. In this method, the coax line does cross he
base insulator intact. But a quarter-wavelength up the AM antenna, the coax line must be
insulated from the tower. This quarter-wavelength is figured at the AM frequency.
These tuned sections work out pretty well, but the spot where the coax shorts to
the tower is reasonably critical if the full advantage of the section is to be realized. Past
the quarter-wave insulated section, the line is bonded directly to the tower the rest of the
way up to the FM antenna. The inner conductor of the coax is not affected since it is
shielded from the AM carrier by the outer conductor of the coax. As far as the AM carrier
is concerned, that coax line is open at the tower base.
Problems can occur if insulators break and allow the line to touch the tower, or if
something shorts out an insulator. This destroys the tuned-line effect and, of course the
insulating qualities. When the tower is painted, these insulators must not be painted, and
anything that can cause leakage, such as ice or corrosion across the insulator can reduce
the tuned line’s effectiveness and affect the AM system.
Whenever an FM antenna is added to an existing, AM tower, a new measurement
of the base impedance of the tower is required, and this must be filled with the FCC.
Additional equipment on the tower, plus crossing the base insulator, will probably affect
the parameters of the antenna.
If the station is to be an AM FM station, even though the FM may be some time
later getting on the air, mount al the FM gear on the AM tower before the base
measurement of the AM tower is made. If you do not, then when you do it some time
later, a new set of measurement must be made.
80
Towers
The tower is an important structure that requires a large capital investment by the
station. A properly designed and installed tower, given the usual care, will stand and
serve for many years. There are many AM towers standing today that are over 40 years
old.
Wind Loading
A tower is designed to withstand a certain amount of wind pressure, and this is
figured with a certain amount of ice coating. The figures are usually conservative. The
tower is usually specifically designed for heavy duty or light duty. As long as the original
conditions exist, the tower will give many years of service.
But many factors can change these original conditions. One factor is the additional
loading on the tower. When antenna’s microwave selectors and similar equipment are
added to a tower, this changes both the weight-loading factor and wind loading factor.
Some of the smaller FM antennas do.
Dead weight-that is, the vertical weight of the equipment-is not important as the
wind-loading, unless of course, the tower is a very light –weight design and the load is a
very heavy antenna. Most towers are carefully designed for the dead weight they can
carry and are designed for certain specific purposes, such as mounting microwave dishes
or heavy TV antennas. If a tower is loaded with all sorts of things it was not designed to
carry, it may be overloaded, and a gust of wind may cause it to collapse. Before
mounting anything large on the tower, consult the factory and get their opinion. They will
be able to determine if the tower can carry the load or not.
Unless a tower is inspected at regular intervals and any faults corrected, it can
deteriorate quickly. Remember that the tower is exposed to all types of weather, heating
and cooling, wind stresses, chemicals born in the air, and salt near oceans. Rust can set
in, braces work loose, bolts fall out. On guyed towers, the guys may lose tension or
break. All these factors change the original conditions, and when a tower is neglected,
these factors can weaken the tower an cause it to come down in a high wind.
Joint Use
It is common practice today for different broadcast companies to share the same
tower, for example, a TV, FM station, or both, on an AM tower. In the past, each use of
the tower was responsible for the lighting, painting, and other FCC requirements.
Agreements must be worked out among all parties and approved by the FCC. The
approved agreement must be kept on file at each of the stations for the radio inspector
to see. All the other stations then don’t have to concern themselves with the
requirements of lighting, painting, and logging of the tower. The one that assumes the
obligation (is usually the tower owner) must comply with all the FCC requirements.
Painting
Towers must be painted in a prescribed manner to provide greater visibility to
aircraft during daylight hours. The prescribed colors are international orange and whit. All
towers are not required to meet this section of the rules. (all these requirements will be
found in part 17 of the rules.)
All towers more than 200 feet above ground level must be painted. Tower less
than 200 feet may or may not be required to be painted. This depends upon their
location in relationship to airports and air corridors. In all cases, the prescribed painting
will appear in the station’s construction permit and license. When the paint begins to
fade, the tower must be repainted. If a station has approval to use the new high-
intensity lighting, the tower may not be painted.
Even short tower whose top is 200 feet above ground must be painted. This would
be the case if a large part of the support structure were a tall building.
Banding
The color of the paint bands and the number and width limits are prescribed in the
rules. The bottom and top bands must be international orange. For towers up to 700
feet, there must be 7 equal bands to alternate orange and white. Towers of greater
height than this must have additional bands since the maximum width can only be 100
feet, and at 700 feet, the maximum width-100 feet- has been reached. The minimum
width is 1 ½ feet.
To compute the number of bands and their width (for towers up to 700 feet),
divide the tower height by 7 to obtain the width of the band. For example, a 350-foot
tower must have 7 bands of 50-foot width. If the tower is 700 feet, each band is 100
feet, the maximum. There will 4 orange bands and 3 white bands.
81
Tall Towers
Since the maximum width of each band can be 100 feet, towers greater in height
than 700 feet must have more than 7 bands. To determine the total number of bands
required, add two bands for each 200 feet of tower above 700 feet. If there is a fractional
part less than 200 feet, add two bands for that fraction. In all cases, the top and the
bottom bands must be orange, so there will always be an equal number of bands in the
total figure.
For example, a 900 feet tower would have 7 bands for the 700 feet plus 2 more
bands for the nest 200 feet, for a total of 9 bands. In another case, lets assume the
tower is 990 feet. You have already worked out 9 bands for the first 900 feet. For that
additional 90 feet, there must be 2 more bands. This would make a total of 11 bands for
the 990 foot tower. The width of each band in the first case will be 100 feet (900/9 =
100). In the second case, the bands will be 900 feet wide (990/11 = 90).
Standard Lighting
A tower which is 150 feet or more above ground level must be lighted according
to the FCC rules. The particular pattern prescribed will be determined by the tower height
or special lighting requirements. Towers less than 150 feet may need lighting. In all
cases, the prescribed lighting for the tower will be shown in the construction permit
license.
Essentially, there is a flashing code beacon on top of the tower, and at differently
intervals on the tower, side marker lights or additional code beacons are required
according to the tower height. These side lights must be seen from all directions. So they
will be mounted on the outside of the tower leg at each interval one on each leg. For
towers of 300 feet or less, there will be one flashing beacon at the top and a set of
marker lights at midlevel. Changes occur in the requirements after every 150 feet of
tower height, with a different arrangement of marker lights and additional code beacons.
Lamps
The flashing code beacons must contain two lamps wired in parallel. Each lamp
must be rated at 620 W or 700 W. Having two lamps in parallel is a safety feature, for if
one burns out there will still be one lit even though the output will be cut in half. The
lamps themselves have clear glass envelopes. The beacon contains a red screen to
produce the red color, and the outside glass of the beacon is a lens which focuses the
light into a horizontal plane.
The marker may burn continuously, or they may be controlled automatically by a
photocell control. The photocell must face the north sky, and when daylight drops to 35
foot-candle, it should turn the lights on. When the north sky brightens in the morning to
58 foot-candles, the photocell may turn the lights off.
The photocell must have an unobstructed view of the north sky. If it is shaded by
a tall tree or building, it will turn the lights on too early and off too late. If the photocell
should fail, it must turn the lights on, and they must burn continuously until the photocell
is repaired. This is called a fail-safe agreement. Towers which are less than 150 feet and
which must be lighted may use a photocell, a clock, or manual control.
Flashing Beacons
The flashing of the beacons must be within the limits prescribed by the rules.
There can be no less than 2 flashes per minute or more than 40. the on or lighted time
must be twice the off or unlighted time. For example, if the lamp is flashing 20 times per
minute, the total on-off cycle will be 3 seconds. The time on time will be 2 seconds, and
the off time will 1 second. This 2-to-1 ratio must be maintained, as must the number of
flashes within the prescribed limits.
The flashing mechanism will require some maintenance. Expect to have problems
with the rotating and switching part of the unit. The flasher can get the station a citation
of the code flashing is out of limits. The inspector does check this.
Installation
The tower lighting will draw heavy current. The wiring runs are long, so heavy
cable should be used to prevent or reduce voltage drop at the top of the tower. Although
100 V may be entering the cable at the bottom, several hundred feet later there may be
100 V left. When the system is first installed and in operation, have the voltage
measurement at the socket of each fixture in the system. The bulbs should be in place
and drawing their share of current. Make note of these measurements for future
reference.
If the socket voltage is too low for the rating of the lamp, its light output will be
lower than normal. The rules require that the rated voltage of the lamp be within 3 % of
the socket voltage. If the condition existed as just mentioned, the lamp must be rated
within 3 % of 110 V and 120 V.
82
High-Intensity Lighting
When a station desires to use high-intensity lighting, it must receive approval
from the FCC. When the FCC does authorize the station to use this system, then it will
replace the requirements for both the standard lighting and the tower painting
requirements of the rules. It must, however, conform to the rules as they apply to high-
intensity lighting.
The high-intensity lamp will produce a light that approximate daylight, with
responses from infrared to ultraviolet. This daylight spectrum is what makes it so and
contributes to its brightness. The lamps are quartz lights filled with xenon gas. The
presence of the gas and the pulsing of the light creates a high light output and high
efficiency. This special fixture with their reflectors also boost the light output so that it
carries a terrific punch.
Light Pattern
The arrangement of lights on the tower depends as much upon the height above
ground as it does in the conventional lighting. Break over points are at 300, 600, and
100 ft. The height in this case is of the tower itself and does not include any antenna as
that are mounted on top of the tower. At each of the height levels on the tower where
they are required including the top of the tower, at least three fixtures will be required,
and maybe more.
The same light output must be radiated horizontally from each level in a 360-
degree circle around the tower without obstructions. This typically requires three fixtures
on a three-leg tower and four on a four-leg tower, but it depends upon the width of the
tower and the ability of the particular fixtures to provide even lighting.
Figure 11-8 shows the relationship of the components of a strobe lighting system.
If an antenna or anything projects above the tower more than 20 feet, a special, single
omni-directional lamp must be mounted on the top of this projection. This is different
from the other fixtures, since it projects light in a manner similar to the conventional
code beacon.
Light Output
These lamps will burn continuously around the clock, but at different intensity
levels. These intensities will change at twilight, at dark, and again in the morning. A
photocell is required to monitor the north sky and operate an automatic changing device.
During daylight, these lamps must produce an output of 200,00 candelas in the
horizontal plane. These intensities will change at twilight, at dark, and again in the
morning. A photocell is required to monitor the north sky and operate an automatic
changing device.
At twilight, when the north sky dims to a light level 30 and 60 foot-candles, the
light output from the fixtures will be reduced to 20,000 candelas; and the north sky dims
to a light level between 2 and 5 foot-candles, the fixture output is reduced to 4000
candelas.
When a top omni-directional lamp is required, its output will be 20,000 candelas
during daylight and twilight hours and must drop to 4000 candelas at night. This light is
controlled by the photocell as are other lights.
Should the photocell or its control device fail, the lights must go to either the
daytime brilliance of 200,00 candelas or the next light step higher than is required for the
amount of daylight.
All the lights in the system must flash simultaneously. The prescribed flashing rate
is 40 flashes per minute. The actual duration of the flash (on time) is 10 milliseconds
during daylight and 250 milliseconds during night.
Power Supply and Control
High-intensity type of lighting requires a power supply and control circuitry. Both
of these are solid-state units that mount at the ground level. They may be mounted in a
building at the tower base or on the tower itself (at the base). The units are housed in a
weatherproof cabinet they can be mounted outdoors. Monitoring units are also available
so that the lights can be monitored and operated by remote control.
83
Sound in Enclosed Rooms
Good Acoustics – Governing Factors
Reverberation Time or Amount of Reverberation: This varies with frequency and is
measured by the time required for a sound; when suddenly interrupted to die away or
decay to a level 60 decibels below the original sound.
The reverberation time and the shape of the reverberation time/frequency curve
can be controlled by selecting the proper amounts and varieties of sound-absorbent
materials and by the methods of application. Room occupants must be considered in-as-
much as each person present contributes a fairly definite amount of sound absorption.
Standing Sound Waves: Resonant conditions in sound studios cause standing
waves by reflections from opposing parallel surfaces, such as ceiling-floor and parallel
walls, resulting in serious peaks in the reverberation-time/frequency curve. Standing
sound waves in a room can be considered comparable to standing electrical waves in an
improperly terminated transmission line where the transmitted power is not fully
absorbed by the load.
Room Sizes and Proportions for Good Acoustics
The frequency of standing waves is dependent on room sizes: frequency
decreases with increase in distance between walls and between floor and ceiling. In
rooms with two equal dimensions, and between the two sets of standing waves occur at
the same frequency with resultant increase of reverberation time at resonant frequency.
In a room with walls and ceiling of cubical contour this effect is tripled, and elimination of
standing waves is practically impossible.
The most advantageous ratio for height : width : length is in the proportion of 1:2
1/3:2 2/3 or separated by 1/3 or 2/3 of an octave.
In properly proportioned rooms, resonant conditions can be effectively reduced
and standing waves practically eliminated by introducing numerous surfaces disposed
obliquely. Thus, large-order reflections can be avoided by breaking them up into
numerous smaller reflections. The object is to prevent sound reflection back to the point
of origin until after several reflections.
Most desirable ratios of dimensions for broadcast studios are given in Fig. 1.
Optimum Reverberation Time
Optimum, or most desirable reverberation time, varies with (A) room size, and (B)
use, such as music, speech, etc. (see Figs. 2 and 3). Figure 3 shows the desirable ratio of
the reverberation time for various frequencies to the reverberation time for 512 hertz.
The desirable reverberation time for any frequency between 60 and 8000 hertz may be
found by multiplying the reverberation time at 512 hertz. (From fig. 2) by the desirable
ratio in Fig. 3 which corresponds to the frequency chosen.
The reverberation time affects the intelligibility of speech unless suitable speech
cadences are developed. The intelligibility at a sound intensity of about 1 dyne/cm 2 is
shown in Fig. 4.
Measurement and Computation of Reverberation Time
The reverberation time of an enclosed space that already exists is an important
quantity that is relatively easy to measure. Such measurements can yield invaluable
information about the space in a more accurate and easier-to-process form that can
calculate only. When the enclosed space does not exist (new construction, for example
except on the architect’s drawing board, it is necessary to use the most accurate method
of calculation available.
The measurement of Reverberation Time
The degree of accuracy is determined by the use to which the data will be put. If
the purpose is merely to compare the reverberation time to one of the existing criteria
charts, the by-car method using a simple automatic switch will often thoroughly satisfy
the requirement. If the enclosed space is a concert hall of significance, the Schroeder-
Kuttruff method is almost mandatory. In addition, in concert hall, the early decay time
(EDT) is of great interest. The majority of day-to-day reverberation measurements are
taken with quite satisfactory results by using the interrupted-noise method.
Using the Ears-and-Stopwatch Method
The ears-and-stopwatch method of measuring reverberation time works best with
reverberation times in excess of 2 seconds. In auditoriums where speech intelligibility is
of importance, the design engineer needs to take careful note of the potential articulation
losses whenever the RT60 exceeds 1.6 seconds. (The RT60 is the time required for the
84
reverberant sound to decay 60 dB.) Below that value, the reverberation time will not
detrimentally affect the intelligibility, although making it too low may require excessive
acoustic power to be generated at the sound source.
The measurement procedure is to excite the space with some steady noise of wide
spectral content. (A random-noise generator, inter-station noise from an FM tuner, a
bursting balloon, or a small yachting cannon all have been employed at different times.)
Care must be exercised to ensure that the noise source exceeds the ambient noise by at
least 30 dB and preferably by the full 60 dB. It is usually wise to band-limit the noise in
some fashion, if possible, especially at the lower frequencies, as it is the region around
1000 Hz and 2000 Hz that affects intelligibility.
The listener stands in the reverberant field, at least 2/3 of the room distance
away from the sound source (Fig. 5). The sound source is usually turned toward a corner
in order to excite the maximum of room modes. When the noise is shut off, the
stopwatch is started, and when the listener judges that the sound has drop to the
ambient noise level, the stopwatch is halted. (Practicing in spaces where the RT60 is
already known will rapidly “calibrate” the ears to a surprisingly accurate degree.) If only
30 dB of decay is available, the time recorded by the stopwatch is doubled. If 60 dB of
decay is available, the time is read directly.
In defense of this deceptively simple method, let it be said that data contains as
high as a 50 % error is vastly more useful than no data at all in engineering a sound
system into an existing acoustic environment.
The Interrupted-Noise Method
The interrupted-noise method of measuring reverberation time is illustrated. This
is the most widely used method and yields excellent field results; only in the most critical
concert halls is this method found wanting. It has been stated by April that the subjective
assessment of reverberation time is governed by the early decay time (EDT, which is the
time it takes the early decay to change by 15 dB). Good agreement between this EDT
and subjective estimates of the presence or absence of excessive reverberation has been
obtained in a number of concert halls. This first 15 dB of decay is difficult to obtain with
the interrupted-noise method because of the statistical variations that occur in the test
signal over short time periods.
The Schroeder-Kuttruff Method
The Schroeder-Kuttruff Method Fig. 7 employs a 2.7-ms rectangular pulse that is
used to excite a standard 1/3-octave bandpass filter. The resulting “ringing” of the filter
provides a statistically reliable signal that allows highly repeatable decay recordings and
excellent resolution of the EDT.
Reverberation-Time Meters
At the present time, at least one manufacturer provides an RT60 meter for
measurement of reverberation time. This device contains in a hand-held carrying case
the measuring microphone, octave-band filters, and a direct-reading signal readout. A
random-noise generator, a power amplifier, and a test loud-speaker are also required.
The first 15 dB of decay is recorded by letting the decaying sound go through two gate
circuits, and the digital readout automatically displays the time for the 15-dB decay
multiplied by 4 for the full 60 dB.
Uses of Reverberation-Time Measurements
The main reason for such extensive efforts to determine RT60 accurately is that
this is the easiest way to find the average absorption coefficient (a) and its associated
value of reflectivity (1-a) in an acoustic environment. Traditionally, the way to increase
intelligibility in an acoustic environment is to increase a.
When an electro-acoustic system is employed in a given environment, an increase
in the directivity factor, Q, of the sound source (see section on public address systems)
can be substituted for increased a over a surprisingly wide range of applications.
Therefore, the contemporary electro-acoustic designer needs to have an accurate a figure
in order to calculate the minimum Q that he requires in the sound sources. A further use
of the evaluation of both RT60 and Q is their role in the establish of an acceptable
articulation loss of consonants in speech. (See section on public-address systems.)
Of greatly increased current interest is the role of a in helping to reduce the
reverberation sound field in an acoustic environment, thereby making the overall sound
level in the space lower than it was before the absorption was applied. It should be
noted, however, that absorptions will not lower the sound level for any listener in the
direct sound field of the sound source.
For a better understanding of the beneficial engineering uses of the
measurements, it is necessary to examine in detail the commonly used equations with
them.
85
The Sabine Equation
At the turn of the century, W.C. Sabine, a professor of physics at Harvard
University, experimented with the correction of a poor acoustic environment by the
introduction of seat cushions taken from an acceptable acoustic environment. As a result
of the experiment, he wrote the first usable reverberation-time equation:
RT60 = (0.49V)/Sa
where RT60 is the time in seconds required for a sound to decay 60 dB, V is the volume of
the room in cubic feet, S is the boundary surface area in square feet, and a is the
average absorption coefficient. The value of a is:
a = (s1a1 + s2a2 + ….. snan) / s
where s1, s2 etc., are boundary surface areas; a1,a2,etc., are the absorption values for
the boundary areas with which they are associated; and snan is the total absorption of the
people, furniture, etc., present in the room. For metric use, the constant 0.049 becomes
0.161, V is in cubic meters, and S is in square meters.
The variation of the reverberation-time are:
a = 0.049 V / (S * RT60 ) ; V = ( S*a* RT60 ) / ).049 ; S = 0.049 V / (a * RT60 )
The Norris-Eyring Equation
By 1930, R.F. Norris recognized that, in the limiting case, the Sabine equation
predicted a finite reverberation time in a room with 100 % absorption present. He further
demonstrated that for true absorption values in excess of 0.63, this equation could give a
values in excess of 1.0 (100 % absorption). In conjunction with C.F. Eyring, Norris wrote
an equation that gave a values from 1.0 to 0 for true absorption values when calculated
from actual RT60 measurements. The Norris-Eyring is:
RT60 = (0.049 V) / (- S ln (1-a)) ; a = 1- exp (-0.049 / S * RT60 )
V = (RT60 ) ( -S ln(1-a) / 0.049 )
S = (0.049 V) / (RT60 ln(1-a))
If the value of RT60 is measured and the corresponding value of a is calculated, insertion
of this value of a into the expression – In (1-a) converts the a value into a Sabine a. For
example, - In (1- 0.63) = 0.99.
When tables of absorption values are examined, it is of vital importance to know
which formula was used in determining the numerical values. If the values were obtained
using the Sabine equation, be sure to use Sabine equation variations consistently for any
further manipulations of the data. If the Norris-Eyring equation was used, remain
consistent in its use for any further manipulation of the data.
In the method illustrated, the absorption coefficient of the test material is
calculated from the equation.
a = (0.049V(1/TM – 1/TE)) / (A1 + A2 +A3)
where a is the absorption coefficient of the test material, V is the internal volume of the
test room in cubic feet, A1 + A2 +A3 is the surface area of the test material, TM is the
measured RT60 of the test room with the test material installed as shown, and TE is the
measured RT60 of the empty test room. If Sm is defined as A1 + A2 +A3, the equation may
be written in the following alternative forms:
Sm = (0.049V)(1/TM-1/TE) / a
TM = 1 / ((aSm/0.049V) + (1/TE))
TE = 1 / ((1/TM) – (aSm/0.049V)) ; V = 1 / (0.049((1/TM) – (1/TE)) / (aSm)
The total Sa is the sum of Sa with the room empty plus Sa of the test sample. As an
example, let Sm = 75 ft2, V = 8000 ft3, s = 2400 ft2, TM = 6.5, TE = 9.0 and a = 0.018 for
the empty room. Then:
a = (0.049 x 8000)((1/6.5)-(1/9.0)) / 75 = 0.223
RT60 = (0.049 x 8000) / ((2400 x .018) + (75 x 0.223)) = 6.8
86
The Fitzroy Equation
The next major improvement in the use of these basic equation came in 1959 with
the publication of Dariel Fitzroy’s paper “Reverberation Formula Which Seems To Be More
Accurate With Non-uniform Distribution of Absorption” in the manual of the Acoustical
Society of America Fitzroy had become concerned with the discrepancies that occurred
between the calculated and measured RT60 when the absorption was not uniformly
distributed about the acoustic environment – for example, if the total ceiling is covered
with highly absorptive acoustic title, but all other boundary surfaces are hard and
reflective. The Fitzroy equation is the same as the Norris-Eyring equation if the
absorption is evenly distributed, but it yields much more accurate answers when uneven
distribution is encountered.
RT60 = (0.049V/S2) [(2xy / (-ln(1-axy))) + (2xy / (-ln(1-axz))) + (2yz / (-ln(1-ayz)))]
Where x and y are the height and width of the room, and axy is the average absorption
coefficient for the two end walls; x and z are the height and length, and axz is the
average absorption coefficient for the two side walls; and y and z are the width length,
and ayz is the average absorption coefficient for the floor and ceiling.
This equation is used only for calculating the expected RT60 from the drawing of
the acoustic environment. Once the expected RT60 from the drawings of the acoustic
environment. Once the expected RT60 is calculated, that value is insert into the standard
Norris-Eyring equation variation to obtain the true a value.
The Fitzroy equation is an invaluable tool in the study of how and where to place
absorbent materials for optimum control RT60.
BASIC CONSIDERATIONS IN THE MEASUREMENT, CALCULATION, AND
APPLICATION OF ACOUSTIC TREATMENT
While the measurement and/ or calculations of RT60 a, etc., can be made today
with acceptable accuracy, these techniques and equations supply only a few hints of the
variations in application of the material itself to achieve the optimum results with the
minimum cost. A few of the more basic rule are listed:
1. Diffusion is highly desirable, and both absorption and room geometry should
be employed to enhance it.
2. Every effort should be made to preserve useful reflecting surfaces (those
within 30 to 50 feet of a sound source).
3. Rarely should absorption be placed on ceilings. Preferred choices include the
floor carpets also lower noise levels at the source as well as providing
absorption-rear walls, etc.
4. It should be considered that too high RT60 will detrimentally affect
intelligibility, and an RT60 that is too low requires much higher power output
to overcome the excessive absorption.
5. Low-frequency absorption is usually controlled by diaphragmatic action and
high-frequency absorption by soft, fuzzy materials.
6. Materials useful as absorbers are almost never useful as isolators. Absorbers
are intended to control the reverberant field within an acoustic environment.
Isolators are intended to keep sound inside a given environment or to keep
sounds in other environments outside of the given environment. Good
isolators are characterized by mass and rigidity. Good absorbers are
characterized by porous ness and non-rigidity.
These room parameters directly interact with the directly factor Q, of the sound
system, and they should be adjusted to optimize the overall room-sound-system
performance.
Public Address Systems
Successful speech and music reinforcement systems require a threefold design
solution:
87
1. The reconciliation of the reverberation time, the directivity factor of the
loudspeaker, and the distance from the sound source to the farthest listener
so that an acceptable articulation loses consonants in speech is obtained.
2. The adjustment of the system parameters, within the limits set forth as
necessary to achieve good articulation, to insure the required acoustic gain.
See Fir. 9.
3. The determination from the first two steps of the electrical power required at
the input of the transducers in order to produce the acoustic power needed at
the listener’s ears.
Basic Definitions
D1 = the distance in feet from the sound source (loudspeaker) to the microphone.
D2 = the distance in feet from the sound source (loudspeaker) to the most distant
listener.
Ds = the distance in feet from the talker (performer) to the microphone.
Do = the distance in feet from the talker (performer) to the most distant listener. See
Fig. 10.
EAD = the equivalent acoustic distance in feet. This is the maximum distance from a
talker that a listener can comfortably stand and hear clearly without a sound system.
EPR = the electrical power in watts required at the input of a loudspeaker to achieve the
specified acoustic level.
r = the distance from the sound source for calculations.
n+1 = the number of loudspeaker groups; n is the number of groups of the same
acoustic power output as “1” group (which supplies direct sound to the listener) not
supplying direct sound to a given single point of observation.
% AL cons = the percentage of articulation loss for consonants in speech. A successful
speech system should not exceed a maximum of 15 % AL cons.
V = the volume of the room in cubic feet.
RT60 = the reverberation time in seconds for 60 dB of decay.
Q = the directivity factor. Also called Ro.
R = the room constant in square feet.
R = Sa/(1-a)
Dc = the critical distance, the distance at which the direct sound level equals the
reverberant sound level.
Lsens = the output of the loudspeaker in dB-SPL at 4 feet for an electrical input of 1
watt.
dB-SPL = the desired acoustic program level at the listener’s ears in dB-SPL.
NOM = the number of open microphones contributing equal input level to the sound
system.
FSM = the feedback stability margin; 6 dB is the minimum considered adequate for
speech purposes.
Key Equations
Adx = -10 log (Q/4pi r2 + 4(n+1)/R) r = Q/4pi 10^((+-)Adx/10) –4(n+1)/R
Dc = 0.141(QR/(n+1)1/2 AD1 + AEAD - ADs – AD2 – 10 log NOM – 6 dB FSM = 0
ADs + AD2 – AEAD + 10 log NOM + 6dB FSM = MinAD
AD1 + AEAD – ADs –10log NOM –6dB FSM = Max AD2
ADs + AD2 – AD1 + 10 log NOM + 6dB FSM = Min AEAD
AD1 + AEAD – AD2 – 10log NOM – 6dB FSM = Max ADs
10 (AD1 + AEAD – AD
s –AD
2 –6 dB FSM)/10 = MaxNOM
%ALCONS = 641.81(D2)2(RT60)
2(n+1)/VQ
Max D2 for ALCONS of 15 % = ((15VQ)1/2 ) / (641.81(RT60)2(n+1))
Max RT60 for ALCONS of 15 % = ((15VQ)1/2 ) / (641.81(D2)2(n+1))
Min V for ALCONS of 15 % = (641.81(RT60)2(n+1)) / (15VQ)
Min Q for ALCONS of 15 % = (641.81(D2)2(RT60)
2(n+1)) / (15V)
Min Norris-Eyring Sa for ALCONS of 15 % = S(1-exp(-1.24D2V/S(15VQ)1/2)
Max (n+1) for ALCONS of 15 % = (15VQ) / ((641.81(D2)2(RT60)
2 )
EPR = 10 (dB-SPLD +10)+(AD2-A4)-L
SENS / 10 Note: for (AD2-A4)
Max Prog Level in dB-SPL from available electrical power = (watts avail/10)-(AD2-A4)
+LSENS
88
System Example
Assume the following values: V = 500,000 ft3, RT60 = 2.5 s, S = 42,500 ft, D2
=125 ft, n+1=2, NOM = 2, LSENS = 110 dB-SPL, EAD desired = 8 ft, dB-SPL= 85 dB-SPL.
Design a system that will fulfill these requirements in an acoustic environment with these
parameters.
Min Q that allows 15 % ALCONS
= 641.81(125)2(2.5)2(2) / (15(500,000)) = 16.71
A standard available unit has a Q of 17, so this is a realizable requirement.
A =1- exp(-0.049V/S* RT60 )
Therefore:
a = 1-exp 0.049x500,000/(42500x2.5) = 0.206
R = 42500(0.206)/(1-0.206) = 11,206 ft2
Dc = 0.141 17(110206)1/2 / 2 = 43 ft
Distance D1 should be 45 ft. This is to insure maximum available acoustic gain
while avoiding time-delay interference. A good D1 selection would be 40 feet. See Fig. 13
This result means that the two talkers should wear lavaliere microphones within
approximately 2 feet of their mouths, and all conditions will be met so far as clarity and
loudness are concerned.
It is now only necessary to insure that the selected pair of loudspeakers with their
individual Qs also provide full coverage of the audience. See Figs. 13 and 14.
The correct place to aim the center of a single loudspeaker Fig 14 in an auditorium
is at the last seat, not at the middle of the auditorium. This is because the last seat
needs the highest Q, and the highest Q exists on the 0° axis of the loudspeaker. The next
problem to consider involves the rear wall and the upper part of the beam. If the wall is
not titled out as its height increases, is not sufficiently irregular to provide diffusion, or is
not highly absorptive (99% absorption only drops the reflection by 20 dB), it will cause
problems no matter what part of the beam strikes the wall at an angle from above is
usually the remedy. Always try to avoid aiming a loudspeaker directly at a wall in such a
way that the on-axis beam is perpendicular to the flat surface.
Fig. 14 illustrates a typical case. Here, the Q is chosen for the last seat, and the
coverage pattern of the loudspeaker is used to insure smooth coverage from the rear to
the front of the auditorium. After the coverage is assured, a quick calculation of the
desired Q for 15%ALCONS at each closer location clearly reveals that determining the Q for
the last seat also does so for all nearer seats, provided smooth coverage is achieved (+-
2dB).
The electrical power required is:
EPR = 10 (85+10)+(33.47 – 10.71) – 110/ 10 = 5.97 watts
This is 5.97 watts per loudspeaker; therefore, since two loudspeakers are involved (for
example, a front speaker and a rear speaker with time-delay correction), the total EPR is
2(5.97), or approximately 12 watts.
It should be kept in mind that the accuracy or sound-system design equations is
predicated on the use of critical-bandwidth, band-rejection, minimum-phase equalizers to
adjust the total transfer function of the sound system to the environment. Failure to
provide for such sound-system-room equalization can lead to large variations from the
predicted results.
References
1. W.C Sabine, Collected Papers on Acoustics, Cambridge (USA); 1923.
2. M.R. Schroeder, “New Method of Measuring Reverberation Time”, Journal of the
Acoustical Society of America, V-1.37, page 409; 1965.
3. B.S. Atal, M.R. Schroeder, and G.M.Sessler, Subjective Reverberation Time and its
relation to Time Decay, 5th International Congress on Acoustics, Liege, Paper G32;
1965.
4. R.F. Norris, “A Derivation of the Reverberation Formula”, published in Appendix II
of V.O. Knudsen’s Architectural Acoustics, John Wiley & Sons, Inc., New York;
1932.
5. D.B. Davis, Acoustical Tests and Measurements, Howard W. Sams & Co., Inc.,
Indianapolis; 1965.
89
103 2 4 6 8 10 4 2 4 6 8 10 5 2 4 6 8 10 5
2
100
8
6
4
2
10
8
6
4
2
1
H
WL
LW
H M
H
W
L
Type Room H:W:LChart
Design-
Nation
Small
Avarage Shape
Low ceiling
Long
1:1.35:1.6
1:1.60:2.5
1:2.50:3.2
1:1.25:3.2
E:B:C
F:D:B
G:C:B
F:E:A
In feet
Volume in cubic feet
Fig.1-Preferred room dimensions based on 2 1/3 ratio. permissible deviation is +-5 %
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
speech only
sound picture theaters
drama
broadcast studio
sound recording
symphony opera
organ only
chamber music solo
Time of reverberation in
seconds
6 8 10 4 2 4 6 8 10 5 2 4 6 8
Volume in cubic feet
Fig. 2 - Optimum reverberation time in seconds for various room volumes at 512 Hz
90
2.0
1.9
1.8
1.7
1.6
Desirable
Ratio 1.5
1.4
1.3
1.2
1.1
1.0
0.9
6 8 10 2 2 4 6 8 10 3 2 4 6 8 10 4
Room volume in cubic
feet
1,000,000
100,000
10,000
1,000
Frequency in Hertz
Fig. 3 - Desirable relative reverberation time vs. frq. for various structures and auditoriums
0 1 2 3 4 5 6 7 8
Reverberation time in seconds
Fig. 4 - Intelligibility as a function of reverberation time.
1.0
0.8
Intelligibility
0.6
0.4
91
Test
Loudspeaker
Power
Amplifier
On-Off
switch
Noise
Source
Observer
with stop
watch
Fig. 5 - The ears-and-stopwatch method.
Reverbmeter
of graphic
level RCDR
Octave-Band
or 1/3
octave-band
filter setSound
level
meter
mike
Random noise
source
Additional
bandpass
filters
On/Off
switch
Power Amplifier
Test Loudspeaker
Fig. 6-The interrupted-noise method
Sound
level
meter
mike
Power Amplifier
On/Off
switch
Test Loudspeaker
Reverb Processor
Graphic Level
Recorder
1/3 Octave filter
set
Fig. 7-The Schroeder-Katruff method
92
Pink-noise
generator
1/3-octave
filter
Power
amplifier
Loudspeakers
Test Material
Reverberation Room
Graphic level
recorder
Microphone
A1
A2
A3
Fig. 8 - Use of a reverberation chamber to calculate a.
2'
amplifierrandom noise
generatorloudspeaker
microphone
amplifier loudspeakermicrophone
SLM
OBA
Test system sound system
Fig. 9 - Measurement of acoustic gain
D1
Do
(A) Single source system
loudspeaker
talker
listener
Ds
mic
93
D1
D2
To closest
loudspeaker
To closest
Do
Ds
(B) Distributive system
20
2
8
3
6
4
1
16
10
600.5
70 80 90 100 110 12050 130
weak
voice
normal
voice
raised
voiceshout
max
vocal
effort
Limit
for
amp.
speechvery
loud
voice
Area where face
to face
communications
are possible using
normal voice
Area where face
to face
communications
are impossible
Area where face
to face
communications
are difficult.
Noise Level (dBA) + 25 dB S/N
Distance
from speaker
to listener
(feet)
D2
4 '
Listener at
distance
positionFig. 12 Calculation of D2
Attenuation
Sound system
loudspeaker
Attenuation of second in dB from 4' in front of loudspeaker to listener = AD2 - A4'
Where, AD2
= -10 log10
(Q/4 pi (D2)2 + 4/R), A4' = -10log
10(Q/64pi +4/R)
94
0
10
20
30
40
50
60
701 2 5 10 20 50 100 200 500 1000
20 log (Dx/Vref)
Distance from sound source in feet
Fig. 13- Decibel changes with distance from source
D3=12dB off
D3=25'
D2=6dB off axis
D2=50'
D1=6dB on axis
D1=100'
L3
L2
RT60
=4.32 seconds
V=500,000 FT3
dB-SPL at 4' = 104
Fig. 14-Loudspeaker orientation (ideal class)
95
(A) Crisscross pattern
(B) Crisscross, 50 % overlap
Floor
50 % Overlap at ear level
Ear level
60o
Fig. 18-Proper distributed density in an overheard distributed sound system.
Ceiling
