The International Telecommunication Union uses an internationally agreed system for classifying radio frequency signals. Each type of radio emission is classified according to its bandwidth, method of modulation, nature of the modulating signal, and type of information transmitted on the carrier signal. It is based on characteristics of the signal, not on the transmitter used.
An emission designation is of the form BBBB 123 45, where BBBB is the bandwidth of the signal, 1 is a letter indicating the type of modulation used of the main carrier (not including any subcarriers which is why FM stereo is F8E and not D8E), 2 is a digit representing the type of modulating signal again of the main carrier, 3 is a letter corresponding to the type of information transmitted, 4 is a letter indicating the practical details of the transmitted information, and 5 is a letter that represents the method of multiplexing. The 4 and 5 fields are optional.
This designation system was agreed at the 1979 World Administrative Radio Conference (WARC 79), and gave rise to the Radio Regulations that came into force on 1 January 1982. A similar designation system had been in use under prior Radio Regulations.
The bandwidth (BBBB above) is expressed as four characters: three digits and one letter. The letter occupies the position normally used for a decimal point, and indicates what unit of frequency is used to express the bandwidth. The letter H indicates Hertz, K indicates kiloHertz, M indicates megaHertz, and G indicates gigaHertz. For instance, "500H" means 500 Hz, and "2M50" means 2.5 MHz. The first character must be a digit between 1 and 9 or the letter H; it may not be the digit 0 or any other letter.[1]
| Character | Description | |
|---|---|---|
| A | Double-sideband amplitude modulation (e.g. AM broadcast radio) | |
| B | Independent sideband (two sidebands containing different signals) | |
| C | Vestigial sideband (e.g. NTSC) | |
| D | Combination of AM and FM or PM | |
| F | Frequency modulation (e.g. FM broadcast radio) | |
| G | Phase modulation | |
| H | Single-sideband modulation with full carrier (e.g. as used by CHU) | |
| J | Single-sideband with suppressed carrier (e.g. Shortwave utility and amateur stations) | |
| K | Pulse-amplitude modulation | |
| L | Pulse-width modulation (e.g. as used by WWVB) | |
| M | Pulse-position modulation | |
| N | Unmodulated carrier (steady, single-frequency signal) | |
| P | Sequence of pulses without modulation | |
| Q | Sequence of pulses, with phase or frequency modulation in each pulse | |
| R | Single-sideband with reduced or variable carrier | |
| V | Combination of pulse modulation methods | |
| W | Combination of any of the above | |
| X | None of the above |
| Character | Description | |
|---|---|---|
| 0 | No modulating signal | |
| 1 | One channel containing digital information, no subcarrier | |
| 2 | One channel containing digital information, using a subcarrier | |
| 3 | One channel containing analog information | |
| 7 | More than one channel containing digital information | |
| 8 | More than one channel containing analog information | |
| 9 | Combination of analog and digital channels | |
| X | None of the above |
Types 4 and 5 were removed from use with the 1982 Radio Regulations. In previous editions, they had indicated facsimile and video, respectively.
| Character | Description | |
|---|---|---|
| A | Aural telegraphy, intended to be decoded by ear, such as Morse code | |
| B | Electronic telegraphy, intended to be decoded by machine (radioteletype and digital modes) | |
| C | Facsimile (still images) | |
| D | Data transmission, telemetry or telecommand (remote control) | |
| E | Telephony (voice or music intended to be listened to by a human) | |
| F | Video (television signals) | |
| N | No transmitted information (other than existence of the signal) | |
| W | Combination of any of the above | |
| X | None of the above |
| Character | Description | |
|---|---|---|
| A | Two-condition code, elements vary in quantity and duration | |
| B | Two-condition code, elements fixed in quantity and duration | |
| C | Two-condition code, elements fixed in quantity and duration, error-correction included | |
| D | Four-condition code, one condition per "signal element" | |
| E | Multi-condition code, one condition per "signal element" | |
| F | Multi-condition code, one character represented by one or more conditions | |
| G | Monophonic broadcast-quality sound | |
| H | Stereophonic or quadraphonic broadcast-quality sound | |
| J | Commercial-quality sound (non-broadcast) | |
| K | Commercial-quality sound—frequency inversion and-or "band-splitting" employed | |
| L | Commercial-quality sound, independent FM signals, such as pilot tones, used to control the demodulated signal | |
| M | Greyscale images or video | |
| N | Full-color images or video | |
| W | Combination of two or more of the above | |
| X | None of the above |
| Character | Description | |
|---|---|---|
| C | Code-division (excluding spread spectrum) | |
| F | Frequency-division | |
| N | None used / not multiplexed | |
| T | Time-division | |
| W | Combination of Frequency-division and Time-division | |
| X | None of the above |
There is some overlap in signal types, so a transmission might legitimately be described by two or more designators. In such cases, there is usually a preferred conventional designator.
The emission designator for QAM is D7W. The D7W comes from Paragraph 42 of the FCC's July 10, 1996, Digital Declaratory Order allowing then ITFS/MMDS stations to use 64QAM digital instead of NTSC analog.The emission designator for COFDM is W7D. The W7D comes from Paragraph 40 of the November 13, 2002, ET Docket 01-75 R&O.It is only coincidence that the QAM and COFDM emission designators are reciprocals.