Types of radio emissions

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; it may not be the digit 0 or a letter.

Types 4 and 5 were removed from use with the 1982 Radio Regulations. In previous editions, they had indicated facsimile and video, respectively.

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.

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