MODULATION TYPES TUTORIAL INCLUDES Types of modulation ITU radio
emission designationsIn order to easily describe the different
types of radio emissions or transmissions, the ITU, International
Telecommunications Union has defined a series of codes that easily
define a radio transmission or modulation format.These ITU radio
emission designations are widely used in the definition of the
types of radio transmission that are used within different portions
of the spectrum and in other areas.These ITU radio emission
designations define the signal - the type of modulation, bandwidth
and the type of information being carried. As such the type of
radio emission, or transmission is defined and not the transmitter
or the system that is used.The ITU designation system was agreed at
the 1979 World Administrative Radio Conference (WARC 79), and
superseded a previous system which has now completely fallen out of
use.
Radio emission types designation formatThe ITU designations for
the different types of radio emissions follows a standard format.
This enables anyone using the system to quickly identify the
parameters of the particular transmission. Although not all
elements of the system may be used every time, it has been
developed so that there is no ambiguity whatever part of the system
for describing the types of radio emission is used.The system has
the following format:
BBBB 123 45
Where: BBBB are characters that define the bandwidth Character
"1" is a letter indicating the type of modulation Character "2" is
a digit that indicates the type of modulating signal Character "3"
is a letter indicating the type of information being transmitted
Character "4" is an optional letter indicating the practical
details of the transmitted information Character "5" is an optional
letter indicating details about any multiplexing, if used.Tables
for the different characters 1 to 5 are given below.
Bandwidth designatorThe bandwidth designator has the format of
three digits that express the significant figures, and a letter
used for the decimal point.The letters used are: H: indicates hertz
k: indicates kilohertz M: indicates Megahertz G: indicates
GigahertzExamples may include 200H for a 200 Hz bandwidth
transmission, 6K00 for a 6 kHz bandwidth, and 1M25 for a 1.25 MHz
wide transmission, etc..
Character 1 - type of modulationThis character describes the
format for the modulation itself. It provides information about the
way in which the signal is superimposed onto the carrier.
LETTERINDICATORDETAILS
ADouble sideband, DSB, including DSB full carrier, i.e.
amplitude modulation
BIndependent sideband, i.e. two sidebands present, each carrying
different information
CVestigial sideband
DCombination of AM and FM or PM, either simultaneously or in a
pre-established sequence
FFrequency modulation, FM
GPhase modulation, PM
HSingle sideband full carrier
JSingle sideband suppressed carrier, SSBSC
KPulse amplitude modulation, PAM
LPulse width modulation, PWM
MPulse position modulation, PPM
NUn-modulated carrier
PSeries of pulses without modulation
QSequence of pulses, phase or frequency modulation within each
pulse
RSingle sideband with reduced or variable level carrier
VCombination of pulse modulation methods
WCombination of any of above
Xcases not covered by the above definitions
It is worth noting that frequency modulation and phase
modulation may also be referred to by the generic term: "angle
modulation."
Character 2 - type of modulating signalThis character of the ITU
designations for radio emissions details the characteristics of the
modulating signal. It provides information including whether the
modulation is analogue or digital and whether there is one channel
of information or more being carried.
LETTERINDICATORDETAILS
0No modulating signal
1One channel containing digital information without the use of
modulating sub-carriers (excludes time division multiplex)
2One channel containing digital information with the use of a
modulating sub-carrier (excludes time division multiplex)
3One channel containing analogue information
7More than one channel containing digital information
8More than one channel containing analogue information
9Combination of analogue and digital channels
Xcases not covered by the above
Character 3 - type of transmitted information This character in
the ITU designation of radio emissions details the type of
information being carried. It provides some insight into the use
and the way in which the information may be decoded.
LETTERINDICATORDETAILS
ATelegraphy for aural reception - e.g. Morse code
BTelegraphy for automatic reception, i.e. machine decoded
CFacsimile
DData transmission, telemetry or command
ETelephony, i.e. voice or music intended for human listening
(including sound broadcasting)
FVideo television
WAny combination of above
XNone of above
Character 4 - details of informationThis character provides some
insight into the format of the information - its coding and
therefore the requirements for decoding he information once it has
been demodulated.
LETTERINDICATORDETAILS
ATwo condition code - elements vary in quantity and duration
BTwo condition code - elements fixed in quantity and
duration
CTwo condition code - elements vary in quantity and duration -
error correction included
DFour-condition code in which each condition represents a signal
element (or one or more bits)
EMulti-condition code in which each condition represents a
signal element (of one or more bits)
FMulti condition code - one character represented by one or more
conditions
GMonophonic broadcast quality sound
HStereophonic or quadraphonic broadcast quality sound
JCommercial, non-broadcast, quality sound (but excluding K &
L below)
KSound of commercial quality with the use of frequency inversion
and/or band-splitting employed
LSound of commercial quality with independent FM signals to
control the level of the demodulated signal, e.g. pilot tones used
to control demodulation process
MMonochrome images or video
NFull colour images or video
WCombination of the above
XCases not covered by the above descriptions
Character 5 - details of multiplexingIncreasingly radio channels
are used to carry more than one stream of information, or they may
be required to share the channel with other users or streams of
information. This character in the ITU designation of radio
transmissions provides information about any multiplexing.
LETTERINDICATORDETAILS
CCode-division multiplex (including code expansion techniques
such as direct sequence spread spectrum)
FFrequency-division multiplex
NNone used
TTime-division multiplex
WCombination of frequency division and time division
XOther types of multiplexingNone of above
