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Electronic Communications
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CHAPTER 1 4.1 Impedance matching ratio of coax balun
Dissipation Factor Indicates energy loss in a capacitor
Quality Factor Indicates energy loss in an inductor
Because of the size of the waveguides
Why is it impossible to use a waveguide at low radio freq?
Losses in the conducting walls of the guide
What causes the attenuation present in waveguides?
Ground Tx lines are either balanced or unbalanced with respect to ___
Spectral Analysis Method of determining the BW of any processing system
50W Average power rating of RG-58 C/u
50 ohms RG-8A/u impedance
RG-211A Coax used for high temperatures
300 ohms 214-056 twin lead characteristic impedance (used in TV lead-in)
AWG#19 Commonly used telephone wire
Quarter wave line Impedance inversion can be obtained in ______
1.2 to 2.8 Dielectric constants of materials commonly used in Tx lines
0.6 to 0.9 Velocity factor of the materials used in Tx lines
Facsimile The transmission of printed material over telephone lines;Emission designation is F3C and A3E
Call waiting tone A continuous tine generated by the combination of 2 frequencies of 350Hz and 440Hz used in telephone lines
10 pulses/sec Pulse dialing rate
VF repeaters Are unidirectional amplifiers having 20-25dB gain placed about 75km apart used to compensate for losses along the telephone line
MTSO Central switching office coordinating element for all cell sites that has cellular processor and cellular switch. It interfaces with telephone company zone offices, control call processing and handle billing activities
Base station Performs radio-related functions for cellular sites in cellular systems
3700Hz Out of band signaling between toll central offices (Bell system standard)
Purely reactive Of SWR = infinite, what type of load the Tx line has?
WATS Standard tariff for flat rate telephone service beyond the normal flat rate in that area
Tariff The published rates, regulations and descriptions governing the provisions of communications services for public use
Varistor A component in the telephone set that has the primary fxn
of compensating for the local loop length
Electromagnetic receiver
Type of receiver used in a conventional telephone handset
0 to 4KHz Ideal passband of a voice-grade circuit using PTN
4KHz Nominal voice channel BW
300 – 3400Hz Telephone channel band pass characteristic
Basic voice-grade The minimum quality circuit available using the PTN
Tie trunk Connects 2 private branch exchanges (PBX)
Trunk line Connects 2 central offices (CO)
3dB Power loss of a telephone hybrid
1897 First Strowger Step-by-Step switch was used in ________
G.122 CCITT recommendation for a preparation of loss plan, a variable loss plan and a fixed loss plan.
1.7x10^-8 ohm-m Copper wire resistivity (ρ)
Umbrella cells Kind of ells appropriate for load management, fast moving mobiles and low usage areas
Adaptive array In cellular networks, standard base station antennas are replaced by _________
Completed The call is _____ when the calling party hears a busy tine on his telephone.
Liable to radiate Short-circuited stubs are preferred to open-circuit stubs because the latter are ______
Quarter wave matching
One method of determining antenna impedance
Quarter wavelength line
It is used as an impedance transformer
The line behaves as a parallel tuned circuit in relation to the generator
If λ/4 Tx line is shorted at one end, ____
Parallel resonant circuit
A shorted λ/4 line at the operating frequency acts like a ____
Series resonant circuit
A shorted λ/2 at the operating frequency acts like a _____
Infinite or an open circuit
The input impedance if a λ/4 short circuited transmission line at its resonant frequency is _____
A high value of resistance
A λ/4 line is connected to an RF generator and is shorted out at the far end. What is the input impedance at the line generator?
Infinite transmission line
Its feature is that its Zin is equal to the line’s surge impedance
Nitrogen Used to keep waveguide dry
Above 3Ghz Waveguides becomes compulsory above _____
50ms Echo suppressors are used on all communication systems
when the round trip time exceeds _____
Insertion of E and H probes into the waveguide
Ways of coupling in and out of a waveguide
Guide wavelength λg (in rectangular waveguides) it is the distance between 2 instantaneous consecutive positions of maximum field intensity;It is always greater then the λo at the same frequency
Waveguides Are Tx lines which can convey electromagnetic waves only in higher order modes;Are hollow structures that has no center conductor but allows waves to propagate down its length;Used mainly for microwave Transmissions because no generators are powerful enough to excite them
At the beginning and at the end of the cable
The outer conductor of the coax cable is usually grounded
Entropy Amount of uncertainty in a system of symbols
Reduced electromagnetic interference
The twists in twisted wire pairs
Inductance Loading means the addition of _____
Coaxial Most commonly used Tx line for high frequencies;Medium least susceptible to noise;Most commonly used Tx line in TV systems
Twisted Pair Medium most widely used in LAN
120 ohms Not a common Tx line impedance
Standing waves A pattern of V and I variations along a Tx line not terminated in its characteristic impedance
antennas At very high frequencies, Tx lines act as ____
DC Blocks It is used in coaxial Tx line to prevent AC power supple voltage from being shorted by a balun or band splitter
Dithering (in TVRO communications) means reducing the effects of noise on the TVRO signal
Freq and Voltage Important quantities in describing waveforms
dNp Known as 1/10 of a Neper
Low attenuation Advantage of a balanced transmission line
Parallel wire line Type of Tx line employed where balanced properties are required
Absorption coefficient
The ration between the energy absorbed by a surface to the total energy received by the surface
The higher the Resistance and The smaller the
The higher the gauge number of a conductor, _______
diameter
λ/4 transformer A short length Tx line used to reduce/eliminate standing waves
Reflectance Ration of reflected power to incident power
CHAPTER 2Sound level meter Instrument used to measure a weighted value of the SPL
(sound pressure level)
Sound An aural sensation by pressure variations in the air which are always produced by some source of vibrations
Noy Unit of noisiness related to the perceived noise level
Phon The unit of loudness level of a sound
Mel Unit of pitch
1000 mels At a sensation level of 40dB, 1000 Hz tone is _____
Sone Unit of perceived loudness
Decibel Measure of the intensity of sound in comparison to another sound intensity
Octaves Much of music is generally referred to in _______
Interval Ratio of frequencies is termed as _______
Pitch and loudness Sound wave’s 2 main characteristics
Pitch A subjective term which is dependent mainly on the frequency and also affected by the intensity
Loudness Or Intensity;Is a subjective effect which is a function of the ear and brain;Loudness depends upon the energy of motion imparted to the vibrating molecules of the medium transmitting the sound;Affected by the distance between the listener and the source and its intensity varies inversely with the square of this distance
Frequency The intensity needed to produce an audible sound varies with ________;The number of vibration or pressure fluctuations per second
Hump and notch Two ways in which the frequency response of a loudspeaker can be varied when it is positioned near a wall
Noise rating values An agreed set of empirical curves relating octave-band SPL to the center freq of the octave bands
Natural freq The freq of a free vibration
Flanking transmission
The transmission of sound from one room to an adjacent room, via common walls, floors and ceilings
Hearing Level A measure of threshold of hearing, expressed in dB relative to a specified standard of normal hearing
330 m/s Velocity of sound in air
341.8 m/s Velocity of sound at room temperature (T=17 deg celcius)
5000 ft/sec Sound wave’s speed in water
Microphone transducer
Converts acoustical energy
Diaphragm and Generating element
2 basic components of a microphone
Expense and fidelity;Complexity and ruggedness;Longevity
Kinds of generating elements
Carbon microphone Operates on the principle that the electrical resistance of carbon granules varies as the pressure on the granules vary
Dynamic microphone Operated by electromagnetic induction that generates an output signal voltage
Crystal microphone Will be damaged if exposed to high temp above 52 deg Celsius
Frequency response Most important specification of loudspeakers and microphones
Bass response IS the bypassing of high audio frequencies
Proximity effect A microphone characteristic that results in boost in bass freq for close microphone spacing
Dolby Noise reduction system used for film sound in movies
Sound intensity Is the sound energy per unit area at right angles to the propagation direction per unit time
Supersonic Speed that is faster than speed of sound
Ultrasonic Sound that vibrates at freq too high for the human ear to hear (over 20KHz)
Wavelength Crest to crest distance along the direction of wave travel
Fundamental Lowest freq produced by a musical instrument
Diffraction Tendency of a sound energy to spread
Refraction When waves bend away from a straight line of travel, it is called _________
Distortion An undesired change in waveform as the signal passes through the device
Exciter Distortion enhances intelligibility when an ______ is added;It is a class of signal processors
Reverberation time Required time for any sound to decay to 60 dB;Time taken for the intensity of the sound energy to drop to one millionth of its initial value
Spider A thin springy sheet of bakelite or metal that permits the voice coil in a dynamic loudspeaker to move back and forth along the core of its magnet
10Hz to 20KHz Bass freq range
20Hz to 20KHz Audio freq range
5KHz to 10KHz High freq range of audio signals
65 dB dB SPL of a voice paging in an office
90 to 85 dB SPL in a church with speech reinforcement only
95 to 100 dB dB SPL in an auditorium with contemporary music
25 to 8000 Hz If the sound waves are converted to electrical waves by a microphone, what is the frequency of the electric current?
Flutter echoes Rapid succession of noticeable echoes
WC Sabine Laid the foundations of acoustic theory of buildings
Threshold of hearing Minimum sound intensity that can be heard
CHAPTER 350 dB The maximum sideband suppression value using filter
system
Noise Is primarily high frequency spikes
H3E Transmits only one sideband;Single side band full carrier emission
A3H Transmits LSB and half of USB;
A3E Double sideband Full carrier emission;Standard way of designating AM
R3E Single side band reduced carrier emission
J3E Single side band suppressed carrier emission;AM system where if m is doubled, the antenna current is also doubled
B8E Independent sideband emission
C3F Vestigial sideband emission;Used in televisions
G3E Phase modulation emission
F3E Frequency modulation emission;Used in FM telephony
F3F Television Emission
F3C and A3E Used in facsimile
F3C Type of emission produced when a frequency modulated transmitter is modulated by a facsimile signal
A3C Type of emission produced when an amplitude modulated transmitter is modulated by a facsimile signal
A3F Type of emission when an amplitude modulated transmitter is modulated by a TV signal
LSB The difference between the RF carrier and the modulating signal frequencies
Baseband freq Produces the sidebands on FM;An information signal that is send directly without modulating any carrier
Spectrum analyzer Test instrument that displays the carrier and the sidebands amplitude with freq to freq
Mixer Also called converter
Buffer Stage in radio transmitter that isolates oscillator from the load
Buffer amplifier Protects the crystal oscillator from ‘pulling’
‘Pulling” Refers to the change of the crystal oscillator frequency by loading
Discriminator Circuit used to detect frequency modulated signals
Carrier signal It has a frequency of 20KHz and above;Has constant peak amplitude
Center frequency The freq of the unmodulated carrier in FM system
Armstrong system One method of generating indirect FM
Reactance modulator One method of direct FM
Direct FM Varactor Diode FM Modulator; Reactance Modulator;Linear IC FM Modulator;PLL with VCO
Direct PM Varactor Diode PM Modulator;Transistor Modulator;
Balanced modulator Circuit
Needed to generate a SSB or DSB signal;Outputs LSB and USB;The output is DSB;It suppresses the carrier;Device that is capable of causing freq translation;Can be used as a phase detector;Lattice modulator – widely used balanced modulator;Product detector – a balanced modulator used to demodulate a SSB signal
Crystal Radio receiver First radio receiver
Non linear Any device to be used as a freq multiplier must be _____
Push-Push amplifier Used for frequency doubling
Frequency synthesizer Frequency division is useful in the implementation of _____
Better fidelity Not an advantage of SSB
Interference to other radio services
Effect of overmodulation in AM transmission
Distortion and splatter Result of the gain level being too high for signals entering the modulator
Base modulation and Collector modulation
Modulation method used for CE configuration
Envelope Detector Most commonly used amplitude demodulator
Rectification Envelope detection is concerned with the process of ___
Distortion Diagonal clipping in envelope detection will result in ____
Coherent signal Has the same Frequency and Phase (but not in amplitude)
Frequency deviation A louder sound, when generating the modulating waveform for FM, will cause a greater ____
Foster Seeley Discriminator
A circuit that demodulates the frequency-modulated signal
Quadrature detector Requires that the inputs are coherent
It is less sensitive to noise spikes;It is less sensitive to interference causing AM
Ratio detector is superior to Slope detector because
3 components A single tone amplitude modulated wave has _____
Continuous modulation
A kind of modulation which the modulated wave is always present
Pulse modulation Type of modulation in which no signal is present between pulses
Coef of modulation Decribes the amount of amplitude change present in an AM waveform
Carrier shift Type of amplitude distortion introduced when the + and – alternations in the AM modulated signal are not equal
The oscillator is crystal controlled
Advantage of PM over FM frequency modulation
AFC A disadvantage of direct FM is the need for
Better S/N ratio;Noise immunity;Capture effectEfficiency of utilized power
Advantage of FM over AM
Wider BW needed;Circuit complexity and cost
Disadvantage of FM over AM
AGC Its function is to maintain the sound volume level of a voice receiver nearly constant for a large single strength range
Noise Blanker Reduces impulse noise in receiver
Frequency translation and up-conversion
If the freq of each component in a signal spectrum in increases by the same fixed amount, this is known as _____
Indirect Synthesizer A frequency synthesizer that contains a single crystal is described as a ________
TRF receiver Receiver in which all RF amplifier stages require manual tuning of the desired RF;Disadvantage is that it has BW variations over the tuning range
Superheterodyne Doesn’t have a modulator;
Receiver An RF amplifier will not be found on every superheterodyne receiver
Image rejection ratio Ratio of the superheterodyne receiver response at the desired fc (carrier freq) to that at the fsi (image freq)
Noise floor of the Rx The limiting condition for sensitivity in a communications receiver
Cross modulation interference
Refers to the condition where the signals from a very strong station are superimposed on other signals being received
Cross modulation An effect which, the modulation of an unwanted signal is transferred to the desired carrier;The modulation of an unwanted signal is heard on the desired signalCan be reduced by installing a filter at the receiver
Intermodulation interference
2 AM transmitting antennas are close together, as a result, the 2 modulated signals are mixed in the final RF stage of both transmitters. What is the resultant effect on the other station?
Connecting a C between the B+ and the lead ground
Motorboating (low freq oscillations) can be stopped by ____
Stray coupling is minimized
Leads should be kept as short as possible in radio circuit so that ____
4 The # of voice transmission that can be packed into a given freq band for amplitude compandored SSB systems over conventional FM-phone systems
Neutralization Prevents the generations of spurious oscillations
Blocking dynamic range
Ability of a communications receiver to perform well in the presence of strong signals outside the band of interest
RF amp;IF amp;AF amp;Mixer
Common to both AM and FM receivers
IF amplifier Determines a communication receiver’s sensitivity
Filter ringing Occurs during CW reception if too narrow a filter BW is used in the IF stage of a receiver
Undesired signals will reach the audio stage
The undesirable effect of using too wide a filter BW in the IF stage of the receiver
3000 Hz In a narrow band FM system, the deviation ratio is commonly 1 and the highest audio freq is generally limited to ____
Desensitizing Refers to the reduction of the Rx Gain caused by the signal of a nearby station Tx in the same freq band
Ensuring good RF Reduces Rx desensitizing
shielding between Transmitter
Presence of a strong signal on a nearby frequency
Cause of Rx desensitizing
BW and NF 2 factors the determines the receiver sensitivity
FM receiver Contains limiter stage, discriminator and de-emphasis circuits;The limiter stage prevents any amplitude modulation of the IF signal;The limiter stage rids FM of noise
2.4 KHZ The degree of selectivity desirable in the IF circuitry of a SSB receiver
Resistor Most amp to break down in a radio circuit
AM detector performs rectification and filtering in the receiver
Approx 2.5 to 1 Ratio of PEP-to-average power during a modulation peak in a SSB phone signal
Higher In most mixers, the oscillator freq is higher than the carrier freq on the input signal
BW of emission and Occupied BW
The BW occupied by the carrier, both sideband and the harmonics
Installing resistive spark plugs
A way of eliminating auto interference to radio reception
BFO Generates an output whose freq differs from the IF by 1KHz;Demodulates SSB or CW signal
Am modulation Same as Linear mixing
Linear Summing Mixing for freq conversion is done with a circuit called _____
FM and double side band AM
Suffers most from selective fading
Capture effect Is the reception blockage of 1 FM phone signal by another FM phone signal
Tuned Circuit A negative half of the AM wave is supplied by a ______ in a diode modulator
By having the carrier vary a resistance
Can produce AM
Variable resistance Amplitude modulators that vary the carrier amplitude with the modulation signal by passing it through an attenuator network is the principle of ________
Diode detector Most widely used amplitude modulator
PIN diode Produced AM at very high frequencies
Switch In a diode ring modulator, the diodes acts like a ___
Differential amplifier The principal circuit in the popular 1496/1596 IC
balanced modulator
Class C The AM signals generated at a low level may only be amplified by what type of amplifier?
Crystals Most commonly used filter in SSB generators
CHAPTER 4PCM Quantizing noise happens in _____
Quantization noise Due to the approximation of the quantized signals
Quantizing noise Noise occurring in the presence of signal resulting from a mismatch between the exact value of an analog signal and the closest available quantizing step in a digital decoder
Thermal Noise /White Noise/ Gaussian Noise/ Johnson Noise
Noise from random acoustic or electric noise that has an equal energy per cycle over a specified total freq band
White noise Is measured on a circuit when it is correctly terminated but does not have any traffic
Thermal Noise An electric noice produced by the thermal agitation of electrons in conductors and semiconductors;Most internal noise comes from this type of noise
Atmospheric noise Noise produced by lightning discharges in thunderstorms;Also known as static noise;Not a great problem above 30MHz;Primary cause is lightning;
Transit time noise Type of noise that becomes a great importance/concern at high frequencies
Impulse noise Noise consisting of irregular pulses of short duration and relatively high amplitude
Man-made noise Is usually from transmission over power lines and by ground waves
Cosmic Noise Noise originating from outside the solar system
Space noise Noise coming from stars and sun
Crosstalk noise Noise that occurs via capacitive or inductive coupling in a cable
Miscellaneous noise Crosstalk due to incomplete suppression of sidebands or to intermodulation of 2 or more freq-multiplexed channels which is unintelligible is classified as ____
Solar flare Large emission of hydrogen from the sun that affects communications
Noise density The total noise power present in a 1Hz BW
Increasing channel BW Not a way of reducing noise
Precipitation static Form of interference caused by rain or dust storms
15 to 160 MHz Industrial noise freq
17 deg Celsius / 290 K Reference noise temp
-90 dBm Reference noise level (relative to 10^-12)
CCIT G. 151 Standard for crosstalk limits
CCITT Rec. G. 172 Standard for intermodulation rates on PCM audio channels
800 Hz Reference freq of CCITT phospohometric noise measurement
Psophometer A device that measures the internal VOC of an equivalent noise generator having an impedance of 600 ohms and delivering a noise power to a 600 ohm load
pWp Unit noise power of psophometer
Nif Noise-improvement-factor
Peak values External noise fields are measured in terms of ____
Level The difference between signal strength at a given point and a reference level
Positive A practical dBrn measurement will almost always be a ____ number
Narrowing the BW Noise can be reduced by ____
uV Noise at the input of the receiver can be as high as ____
Mixer Contributes most of the noise in a receiver
MESFET Transistor with the lowest noise figure in the microwave region;Most commonly used in the microwave freq due to its low noise char
11 years The solar cycle repeats the period of great electrical disturbance approx every ___
CHAPTER 5Field strength Amount of voltage induced in a wave by an
electromagnetic wave
James clerk Maxwell Profounded electromagnetic radiation theory
Transequatorial propagation
Is best during afternoon or early evening
UHF and VHF Most affected by knife edge refraction
Kennely-Heaviside Layers
D,E,F layers
D layer Layer that reflects very low freq waves and absorbs medium freq waves (RL,AM)
E layer Layer used for high-freq day time propagation;Layer that aids MF surface-wave propagation a little and reflects some HF waves in daytime
F2 layer Layer that does not appear at night;Reaches a height of 255 km at night
Band Different grouping of electromagnetic spectrum
Reflection Multipath Fading due to interference between direct and reflected rays
Critical freq The highest freq that can be sent straight upward and be returned back to earth
Scatter angle In troposhepric scatter propagation, the attenuation is dependent on ___
Fading Applies to troposcatter propagation;Defined as the fluctuations in the signal strength at the Rx
UHF Tropospheric scatter is used with freq in the following range
Troposcatter propagation
Means of beyond the LOS propagation of UHF signals;It is where 2 directional antennas are pointed so that their beams intersect at the troposphere
Ducting Super refraction; Occurs in troposphere
Duct Layer of warm air trapped above cool air
Shadow zone Absence of reception
SID Sudden ionic disturbances
Lengthen the skip distance
If the Tx power remains constant, an increase in the freq of the sky wave will
Plane wave Radiowave that is far from its sources is called ____
Wavefront A fixed point in an electromagnetic wave
1W VHF ship station transmitters must have the capability of reducing carrier power to ____
It is more pronounced at wider BW
How does the BW of the transmitted signal affect selective fading
Spread spectrum communication
A wide-BW communications systems in which the RF carrier varies according to some predetermined sequence
Approx 300M m/s Speed of electromagnetic waves travel in freespace
VLF waves Are very reliable and are used for some types of services
Affected by the solar cycle
High freq waves
Freq diversity Best solution to ship to ship fading;2 or more Rx are used using a single antenna;
Space diversity 2 or more antennas are used separated by several wavelengths;Best solution to fading
Window Range of microwave freq more easily passed by the atmosphere than the others
Their freq The absorption of a radio wave by the atmosphere depends on _____
Frequency When a beam of light enters one medium from another, a quality that never changes is its
Attenuation As electromagnetic waves travels in free space, this can happen to them
X-rays Highest freq can be found here
Blue Shortest wavelength
Pitch Quality in sound that corresponds to color in light
Dispersion Is the splitting of white light into its component colors in refraction
8000 lx Minimum illumination recommended for reading
Direct wave Microwave signals propagate by way of the ____
Refracted Ionosphere causes radio signals to be ___
2∏ sr The solid angle subtended by a hemisphere about its center is ____
ELF, VLF, MF Uses surface wave propagation
Sky wave The type of radio wave responsible for long-distance communication by multiple skips is the _______;____ gets in contact with ionosphere and reflected by it
HF (3 Mhz to 30 Mhz) LOS communications is not a factor here;Ionosphere has the greatest effects on this range of freq
MF (300Khz to 3 Mhz)
Ground wave is most effective in _____
CHAPTER 6Discone antenna Has vertical polarization;
Radiation pattern is omnidirectional
Bay A section which would be a complete antenna by itself
UHF and VHF Range of freq where most omnidirectional horizontally polarized antennas are used
Critical phased array It is where the current ratios of 2 or more elements must be held at 5% and the phase angle at 3%
Antenna Device that converts high freq current into electromagnetic wave
Antenna array An antenna with a number of λ/2 antennas on it;An underground antenna near the ground acts as a ______
Dipole antenna Radiation pattern in bidirectional;Antenna that is not grounded at one end
Yagi Uda Antenna that doesn’t use the ground
Elementary doublet Antenna which is 1/10 wavelegth long
Broadside antenna An antenna array which is highly directional at right angles to the plane of the array
Marconi antenna Antenna that radiates an omnidirectional pattern in the horizontal plane with vertical polarization;Length = λ/4;Maximum current is found at the base of the antenna;Not a wideband
Parabolic Dish antenna
An antenna with very high gain and very narrow BW
Notch antenna An open-ended slot antenna
Rhombic antenna Non resonant antenna;A properly terminated antenna;Used primarily for skywave propagation
Horn antenna Antenna that is best excited from a waveguide
Resonant antenna Antenna that is not properly terminated
Helix antenna Must have minimum of 3 number of turns
Vertical loop antenna
Has a bidirectional radiation pattern in the horizontal plane
Vertical λ/4 antenna Antenna that provides maximum radiation to all surrounding points in the horizontal plane
Half wave antenna Voltage nodes are located at the feedpoints;Current nodes are located at the ends
Long-wire antenna Antenna made up of a number of full wavelenths
Good grounding A must for vertical antennas
Azimuth Is the horizontal pointing angle of an antenna
Null Very low signal strength in antennas
BEAMWIDTH Measurement of a unilateral antenna properties of directivity;Is the angle between the half power radiation points
Top loading Used in antennas to increase effective height;Improves radiation efficiency
Collinear All elements in a beam ________ antennas are in line
Lightning Rods Must be mounted on top of a structure not les than 30 cm above the highest point
200 kph Estimated medium wind loading in the Phil for antenna tower design
Parasitic element Improves antenna directivity;Gives the antenna unidirectional properties;Increases the antenna’s power gain (for a Hertz Dipole)
FB ratio Comparing the signal strength arriving at the driven element from the desired direction to the signal strength reaching the driver from the opposite direction
End effect Shortening effect of an antenna that makes it appear as it were 5% longer
Low pass filter Are harmonic suppressors connected to an antenna
Increases antenna’s effective length
Add inductor in series
Decreases antenna’s effective length
Add capacitor in series
Stacking antenna elements
______ in a transmitting system will increase field strength at the Rx and increase the directivity of the Tx antenna;Increases sensitivity to weak signals
Driven element The element fed by the transmission line;λ/2 is its electrical length in an HF beam antenna
BW increases If the antenna is shortened through the use of loading coils
Wave straps in the antenna circuitry
Eliminates strong interference from one particular station by the use of this
Trap antennas Disadvantage is that it will radiate harmonics
300 ohms The input terminal impedance at the center of a folded dipole
Antenna efficiency = (radiation resistance / total resistance ) x 100%
Directivity gain Ratio of max radiation intensity to average radiation intensity
Location of antenna wrt to nearby objects
Factors that determine the radiation resistance of an antenna
Protection of personnel working underneath
Reason for using metal counterpoise when antenna is false
Prevent re-radiation of the LO
Reason for using antenna coupler
Diplexer Antenna coupling unit
Long periodic Useful as a multiband HF receiving antenna
CHAPTER 710 to 1000uW Typical speech power
1000 to 3000 HZ Max intelligibility for voice freq is located between
250 to 500 Hz Max voice energy is located between
Volt unit meter Device used to measure speech volume
300 to 3400 Hz Standard freq BW for voice transmission
4000 Hz Standard voice channel spacing
1300 ohms Resistance limit for #2 crossbar exchange in US
0.51 dB/1000ft AWG#26
Loss: 3dB/15ft RG-58 cable
-42 to -52 volts Telephone set voltage sent by CO
3W Typical power output of a cellular phone
825 to 845 MHz Cellular phones transmit in the band from ______
870 to 890 MHz Cellular phones receives in the band from ______
890 – 915 MHz The mobile-to-base frequency assignment for GSM System
45 MHz Frequency separation between the transmit/receive channels
30 KHz Frequency separation between the recieve/receive channels
825.015/870.015 MHz
Channel 1 Transmit/Receive frequency
666 # of transmit/receive channels in the cellular system
80 km The transmission range of cellular telephony
13 miles Range of cellular CDMA System
50 dB Sensitivity of a cellular receiver
± 12KHz Freq deviation of cellular telephone system
Large service area Not an advantage of cellular telephony
Full duplex A cellular phone operates in FD
Half duplex Radio communications between points using a single share freq
Radiotelephony Type of communication when the human voice and music are transmitted
Singing Caused by excessive + feedback;Echo that is completely out of control
Roaming The signal quality of the calls is constantly monitored by the base station, when the quality if the calls drops below a certain specified level, the base requests the MTSO to try and find a better cell site
25 second Time it takes a facsimile to transmit a standard page
Electrolytic recording
A kind of recording used by facsimile
Skewing Distortion in facsimile
Crosstalk Causes a herringbone pattern in facsimile
Acoustic coupler Converts electric signals to audio signals
Hybrid circuit Converts 2wire to 4wire
2wire circuit A circuit usually in the subscriber loop, between the telephone set and the CO
4wire circuit Is used between serving CO for long distance connections with one paro being used for each direction of transmission
Local loop A 2wire or 4wire communication circuit between the customer’s premise and the CO
Subscriber’s loop Physical connection between the tel set and the switching equipment
Trunk line Connects 2 COs
MTSO Linking point between a cell phone and a regular telephone;All of the base stations are linked together by _____ which serves as the CO and management node for the group;Master control center for cellular telephone system;Controls the power of a cellular radio
Cell site Provides interface between the mobile tel switching office and the mobile units
Janyes maximum entropy principle
____ of a data reduction says that when reducing a set of data into the form of an underlying mode, one should be maximally non-committal wrt the missing data
Discrete channel Combination of modulator, channel and detector
1.88 – 1.90 GHz Freq of DECT
12 # of simultaneous calls DECT system can support
120 # of simultaneous calls DECT radio transceiver can assess at a given time
1983 Cellular mobile system was first operated in ______
1000 TACS is a cellular system with ____ channels
6000 Hz SAT (Supervisory Audio Tone) freq is _____
100,000 System capacity of AMPS
Digital-AMPS (D-AMPS)
The voted cellular digital standard
416 # of channels for Band A and for Band B in D-AMPS
Numeric Assignment Module
NAM
Private Automatic Branch Exchange
PABX
Pilot carrier signals Signals designed to keep the receivers and transmitters aligned
Loop extender A device that increases the battery voltage on a loop and extends its signaling range
12 Under ordinary circumstances, the CCIITT recommends that the # of circuits in tandem must not exceed _____
First selector Responds to the request if a subscriber by sending a dial tone
Section The other name of class2 office in the NA switching plan
Small area A cell in the cellular tel system means ____
Cell splitting Single cell subdivided into smaller cells
Circle First cell shape
Repeater Each cell contains a ____
60 degrees Beamwidth of the reflector of the Rx antenna in the base station
Hailing channel Or Calling channel
Erlang Is equal to the # of simultaneous calls originated during a specific hourly period
Erlang B The traffic model about blocked calls clear condition specified blocking probability
Erlang C The traffic model about blocked calls delay condition specified delay probability
Poisson The traffic model about blocked calls held condition specified the held probability at the a time period equal to an average holding time
Volume A method of expressing the amplitudes of complex non-periodic signals such as speech
Echo suppressors ___ is a voice operated device that inserts a high loss in the opposite direction of transmission of the talking party
Double spotting ___ is the picking up of the same station at 2 nearby points on the receiver dial
TPS The type of connector arrangement wherein a customer may move to another location and still retain the same tel number
CCD Most commonly used light sensor in modern fax machines
1500 and 2300 HZ In FM Fax, the frequencies for B&W are ____ respectively
Vestigial sideband AM
Modulation used by Group2 Fax
QAM Modulation used by Group3 Fax
56 Kbps Transmission speed of Group4 Fax
Group3 Fax Most widely used fax standard
Thermal Most fax printers are of which type?
CCITT The one who set up facsimile standards
Satellite weather photos
Type of graphics commonly transmitted by radio fax
Modified GSM The system used by PCN (Pesonal Communications Network)
Termination Refers to - load connected to the output end of a transmission line
CHAPTER 8Optical Fiber Not suitable for CSMA Operation
Transducer Used to convert time varying electrical quantity to an appropriate form
2520 KHz U600 BW
2728 KHz L600 BW
600 AT&T Master Group
300 CCITT Master Group
Hybrid Data Refers to the combined digitally encoded signals transmitted with FDM signals as one composite baseband signal
L carrier system Transmit frequency-division-multiplexed VB signals over a coax up to 4000miles
56KHZ Guard Band between supergroup 18 and supergroup D25
1800 VB Channels A radio channel is composed of ___
Zero bit insertion The transparency mechanism used with SDLC is called ____
2B + D Equation that defines the composition of an ISDN basic access line
64 Kbps Data rate of ISDN basic B Channel
16 Kbps Data rate of ISDN basic D Channel
3 # of channels on which different operations can occur simultaneously on one ISDN basic access line
SDH (Synchronous Digital Hierarchy)
A digital network where voice, video, text and data are multiplexed into a single network for processing and are transmitted prior to use
Terminal Adapters Non-ISDN equivalent can be connected to ISDN line by the
use of ____
213 to 552 KHz;BW = 240 KHz
Baseband freq of standard FDM basic supergroup
Bipolar What is the Transmission signal coding for T1 carrier?
Interfaces the Digital Terminal Equipment to analog communications channel
Purpose of the data modem
DTE (Data Terminal Equipment)
The LCU (Line control Unit) operates on the data in digital form and is therefore called ____;A system that performs // to serial and serial to // conversion of data link;
10Mbps Ethernet is baseband system using CSMA/CD operating at ____
CSMA/CD Before attempting to transmit data, each station has to listen to the channel;With ____, a station monitors the line to determine if the line is busy
Manchester A type of digital encoding technique used to detect collision in CSMA/CD
Channel Accessing Mechanism used by the station to gain access to LAN
Common Channel Signaling
Signaling method relating to a multiplicity of circuits is conveyed over a single channel by labeled messages
LAN Is data communications network designed to provide 2-way communications between a large variety of data communications terminal equipment within a relatively small geographic area
Bridge Interconnects LAN having identical protocols at the physical and data link layers
Router Interconnects LAN having identical protocols at the physical and network layers
Gateway Interconnects LAN that has totally different protocols and format
Parallel Data All bits in a character can be sent/received simultaneously.
Serial Data The bits in a character which are send/received one at a time
Parallel transmission Also called parallel by bit;Also called serial-by-character;
1500m Use of coax cables in interconnecting networks is limited to an overall length of ____
Packet Switching Hold and forward network
Message Switching Store and forward network
Baseband Tx Uses TDM;Transmission where the data are inputted directly on the
cable (data on cable);Medium is a single channel;
Broadband Tx Uses FDM;Transmission where the data are inputted inside the carrier wave (data on carrier);Medium is a multiple channel
Noise is amplified with voice when an FDM system is used
Reason why FDM is being replaced by TDM
Quadrature multiplexing
The process that uses the orthogonality of sines and cosines that makes possible to transmit and receive to different signals simultaneously on the same carrier freq
Start/stop mode Is the mode of transmission in public data network in which data are transferred from source to the network then to the destination in an asynchronous data format
On/Off Keying Amplitude shift keying is also known as _____
Source Coding Circuit the performs the inverse mapping and delivers to the user destination, a reproduction of the original digital source output
2B1Q Encoding The type of encoding used in the Tx of data on an ISDN line between a customer’s premises and a carrier’s central office
Huffman Code A source code whose average word length approaches the fundamental set by the entropy of a discrete memory source
Morse code Code that used three unequal length symbols, dot, dash and space to encode a character
Emile Baudot Developed the fixed-length binary code for telegraphy
Alex Reeves Inventor of the PCM for digital encoding of speech signals
1950 Year where computers and terminals start communication with each other over long distances
1983 Year ISO (International Standardization Organization) adopted the 7layer OSI (Open System Inteconnection) model
ISO 7809 A standard that combines previous standards 6159 and 6256 and outlines the class of operation necessary to establish the link level protocol
PRNET Store and forward Multiple Access Network
TMS Digital switching concepts that can handle more channels
DCA Who promulgated communications-related military standards (MIL-STD)
ARQ Error control used in high freq radio data transmission
EIA Electronic industry association
PDN (Public Data Network)
A communications network designed for transferring data from one point to another
20 Kbps RS-232 is normally an interface between DTE and DCE, what is its signal rate?
Smart mOdems Accepts commands from the terminal via RS-232 interface
FSK Used by slow speed modems
25 Rs-232 has ____ number of PINS
Flexible size Most significant advantage of modular switch over time-and-space switch
Aliasing The overlapping of the original spectrum and the first translated component
Folding freq The highest theoretical freq that can be processed at a sampling rate without aliasing
64 Kbps Basic speed of a digital system
Large BW is required;Requires ADC, DAC;Incompatible with existing analog facilities
Disadvantage of PCM systems and digital transmission systems in general
PCM System A digital transmission system
Quantizing noise Present in PCM systems;The difference between the original and reconstructed signal
Sampling;Quantizing;Coding
Steps to follow to produce a PCM signal
1200 Kbps CCITT V.26 Modems has a modulation rate of ____
Data in video Not a hybrid data
Much better noise immunity
Advantage of PTM over PAM
Dynamic range The ratio of the largest possible magnitude to the smallest possible magnitude that can be decoded by the DAC
Polling A transmission system for a multidrop system;When one station is designates as a master and the rest of the stations are considered as slaves, message handling is _____;Is an invitation by the primary to the secondary equipment to transmit a message;
Echoplex Mode of transmission that achieves less than Full duplex but more than half duplex
Line protocol Rules governing the transmission of digital information
Agreed upon in advance between
Codes must be ___
sender and receiver
ASCII Has 132 chars including 32 control chars;Has 7 bits;Means terminals using asynchronous transmission in ASCII;Most widely used data communications code
EBCDIC Character code that is used without parity;8 bit character code
32H SYN Character of EBCDIC code
Baudot code Fixed length 5 char code;Requires shift characters to provide sufficient combinations;
Framing Is concerned with the boundaries between characters
The end of packet framing
A packet format has an error detecting code at the ____
Asynchronous Transmission
Is less efficient but simpler
Modem Hardware used when the host computer and the terminal are in separate locations;Referred to as a DCE (digital communications equipment);Equipment that interfaces the DTE to the analog Tx line
Null modem A device that connects 2 DTEs directly by emulating the physical connections of a DCE
Low speed modems 2400 bps
Medium speed modems
2400 – 4800 bps
High speed modems 9600 bps
Front end processor Is the data communications hardware that assists the host computer in handling input and output tasks
Equalizer D to A synchronous modems send signals to the ____;The D to A converter in a synchronous modem sends signal to the ____;
Adaptive equalizers Provides post equalizations to the received analog signal;The receive equalizer in a synchronous modem is called ____;The D to A converted in a synchronous modem is called ___;
Amplitude delay Compromise in equalizer settings typically affect ____
Line equalizing A means of improving the quality of a private line ckt by adding amplifiers and equalizers to it
D to A converter Input for a PCM decoder circuit is a series of bits;Output for a PCM decoder circuit is a parallel output of binary coded signals
Gray code Binary codes are transformed in modems into ____
Protocol Analyzer Best type of data communications test equipment
Intelligent terminal Which computer terminal can be programmed to perform
new functions
Unknown The # of bits that are zeros on each symbol when one is transmitting odd-parity coded symbols
FSK A digital modulation technique that results in 2 different frequencies representing binary 1 and 0;Used by Bell 103/113 series for full duplex, 2 transmission speeds of 1 to 300 bps
H-factor Defined as the figure of merit to express degree of modulation in an FSK modulator
Novell Netware ___ is a network operation system with several buildings in compound
Delta modulation Alternative way of digitizing analog signals
3.32 dits 1 bit = ____
Bit rate Rate of change at the input of the modulator
Serial printer Prints 1 char at a time
Impact printer Strikes a ribbon against the paper to produce character images
Bisync Character oriented protocol
STX Start of bisync
X.75 Protocol for packet switching network
Isosynchronous transmission
When asynchronous data are used with synchronous modems
Asynchronous data With _____, each character is framed between a start and stop bit;0 – start bit;1 – stop bit;It is a character oriented protocol
Synchronous data With ___, rather than frame each character independently with a start and stop bit, a unique synchronizing char called SYN is transmitted at the beginning of each message
Overhead Characters that must be transmitted other than the data are called ____
Flag field Used to achieve character synchronization in SDLC
Flag Denotes the start and end of a data link frame
01111111 Go ahead sequence
CRC-16 In USA, it is the most common CRC cocde
Activate RLSD Training sequence (a bit pattern used to synchronize the receive modem) accomplishes one of the ff fxns
low band channel Channel in the 103 modem that occupies a passband from 300 to 1650 Hz
DISC A command that places a secondary station in the normal disconnect mode
Start/stop mode A mode of Tx in public data network in which data are transferred from source to the network to the destination in
an asynchronous data format
IEEE 802.3 CSMA/CD
IEEE 802.4 CSMA/CA
IEEE 802.5 Token passing for Bus Topology
3 How many OSI layers are converted under the X.25 standard
Handshaking Technique involving signaling by both ends of a link to ensure correct data transfer
Scrambler Found in the Tx section in a synchronous modem
XON/XOFF Is a method of flow control
CTS An example of outband signaling is _____
I series CCITT standards that refer to various aspects of ISDN
I.120 I-series that describes what an ISDN is
V series CCITT standard concentrating on data communications over the telephone network
V.14 A recommendation which allows a synchronous modem to be used to transmit asynchronous characters without error control
V.24 A CCITT recommendation which gives definition for the interchange circuits of DTE and DCE
V.26bis Defines a 2400-bps, PSK, half duplex, modem operating at 1200 bauds
V.100 Describes the interconnection between PDNs and PSTNs
X.200 Standard for the 7layer model of OSI
RS-232, RS-350, RS-449, V.21, V.24
Examples of standards for interfaces between terminals and modems
1800 Hz Western Electric 2911 modem operates with a carrier frequency of
Bipolar Violation Occurs when 2 successive pulses have the same polarity and are separated by a zero level
Flow control Process of starting and stopping the terminal output to avoid loss of characters by the receiving stage
Buffering Temporarily storing data to allow for small variations in device speeds
XMODEM Popular PC protocol
ZMODEM Protocol that adjusts its block size based on the lone error rate
DEREP-RB Not a common DNA Repeater
Computer data Data communications refers to the transmission of ____
Bus Fastest LAN topology
Application-independent interfaces
Characteristic of LAN
Cable TV system Not a LAN
Fiber optic Tx Cannot be provided in a broadband LAN
PBX A small telephone switching system that can be used as a LAN
Digital PBX A LAN architecture that can be expanded to the greatest total system BW
Telephone Not primarily a type of data communications
1,0 Mark frequency, space frequency
Noise Cause of errors in data transmission
VRC Other name for parity
LRC Produces BCC (block check char)
QAM Combination of ASK and QPSK
XNOR Not a part of QAM modulator
Redundancy Not commonly used method of error detection
Balanced demodulators
A basic modulator/demodulator circuit in PSK
30 stations per segment
Limitations of 10Base2 network
Logical Not an important char of the physical layer
CHAPTER 9RADAR Radio detection and ranging
ADF Automatic direction finder
DME Aircraft navigation system that determines the time-to-station (TTS) or time-to-go (TTG)
EADI Electronic altitude and director indicator
SONAR A shipboard equipment which measures the distance between the ship’s bottoma dn the ocean floor
Terrestrial Flight Telephone system
An inflight system that allows passengers to make tel calls, send faxes, and play computer games etc
1300 HZ RF carrier of the middle marker is ____
43,500 MHz Freq a radio altimeter operates on
K x 4000 miles Re used in communications design
The pulse width IF Bandwidth is inversely proportional to ____
Space diversity Method applied to reflective path to reduce fading;____ transmission means transmitting and receiving on 2 or more antennas operation on the same frequencies
Freq diversity Method applied to overcome multipath fading of microwave system over water;Method where the signal in transmitted on 2 different freq over the same path;
Litz wire Wire used to reduce skin effect
TWT (traveling wave tube)
Consists of electron gun, helix and collector;Advantage over Klystron for microwave amplification is wider BW;Used at freq in the order of 8000 MHz
Helix The electron beam in a TWT is density modulated by the _____
Wide BW Major advantage of a helix traveling wave tube
Prevents oscillations Attenuator’s purpose in TWT
Klystrons Replaces TWTs in high power amplifiers
At the cathode end of the helix
At what position is the input signal inserted into a TWT
Maintain the desired klystron frequency
In radar set receivers, an AC AFC system may be used to ______
Magnetron Most widely used radar transmitter component;Most common application is in radar;Is only used as a oscillator;A high power microwave pulse of the order of MW can be generated by a _____
Reflex klystron Used as a oscillator;Low power Gunn diodes are replacing _____
Catcher cavity In a klystron amplifier, velocity modulation of the electron beam is produced by the ____
Cavity resonators Sets up the operating frequency of klystrons and magnetrons;A half wavelength, close section of a waveguide that acts as a // resonant circuit is knows as a ____;Is equivalent to an LC resonant circuit
CRT Not a microwave tube (TWT, Klystron and Magnetron)
Tunnel Diode Does not ordinarily operate with reverse bias
Gunn diode Low power radar transmitters and receivers use which component?;A popular microwave oscillator
Varactor and step recovery diode
Widely used in frequency multipliers
Hot carrier diode A popular microwave mixer diode
Attenuation due to water vapor and oxygen
Considered as atmospheric attenuation
60 GHz Freq where oxygen causes excessive attenuation
183 GHz Freq where water causes excessive attenuation
10 GHz Rainfall becomes an important factor in fading of radio waves at frequencies above ___
Slow fading Attenuation that occurs over many different wavelengths of the carrier;Not due to multipath;
Large reflector Causes multipath or frequency selective fading
Delayed Spreading Causes intersymbol interference (in microwave Tx that uses digital radio)
6th Theoretically, electromagnetic radiation field strength
varies in inverse proportion to the square of the distance but when the atmospheric attenuation effects and the absorption of the terrain are taken into account, the attenuation can be as high as the inverse ____ power of the distance
54 The CCIR hypothetical reference circuit covering a distance of 2500 km consists of how many hops
Waveguides Are transmission lines which convey electromagnetic waves in highest freq;They act as a highpass
The cut-off freq if a waveguide
The lowest frequency the waveguide operates
Probe Introduces magnetic field into the waveguide
Periscope antenna Advantage is that it shortens the waveguide’s length
Flattening of equivalent’s curvature (EC)
As the value of k increases, ____ happens
Towards the earth If k-factor is greater then 1, the array beam is bent ____
Phased array A radar antenna using multiple dipoles or slot antennas in a matrix with variable phase shifters is called an ____
PPI Most common radar display;Has an aquadag coating on the inside of the tube (to act as a second anode)
Both lower antenna rotation speed and higher pulse repetition
The display on the PPI scope of a radar set will have greater intensity under the following conditions:
Horn and parabolic reflector
Most radar antennas use ____
Horn antenna Most widely used microwave antenna
Antenna directivity The ability of a radar to determine the bearing of a target
Spark gap Component in a duplexer that protects the receiver from the higher transmitter output
Doppler effect Measures speed;The freq changes;
0.6 The optimum clearance from an obstacle in a microwave system is accepted as ____ of the first fresnel zone radius
Infinity The microwave beam curves the same than that of the earth when the value of the correction factor k equals ____
Baseband repeaters An active microwave radio repeater that can provide drops and inserts
Decrease in resonant frequency
Decreasing the volume of a cavity causes a __________
PCBs Stripline and microstrip transmission lines are usually made
with ____
High loss Coax cable is not used for long microwave Tx because of its ____
Mobile radio Not a common microwave application
1GHz to 100GHz Range of microwave frequencies
Higher cost equipment
Not a disadvantage of microwave
Greater Tx distances A main advantage of microwave
LF band LORAN-C operating freq lies on the ____
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