Types of radio emissions
ITU system for classifying radio emissions by signal characteristics.
The International Telecommunication Union has a standard way to label radio signals. Each emission is sorted by its bandwidth, how the main carrier is modulated, what the modulating signal looks like, and what kind of information the carrier carries. This system is based on the signal’s traits, not on the equipment that sends it. A full emission label looks like this: BBBB 123 45. The first part, BBBB, is the signal’s bandwidth. The next character (1) is a letter that tells what kind of modulation is used on the main carrier—subcarriers don’t count here, which is why FM stereo gets labeled F8E instead of D8E. The second character (2) is a digit that describes the modulating signal, again just for the main carrier. The third character (3) is a letter for the type of information being sent. The fourth (4) is an optional letter for practical details about that information, and the fifth (5) is an optional letter for the multiplexing method. This system was agreed upon at the 1979 World Administrative Radio Conference (WARC 79) and became part of the Radio Regulations that took effect on 1 January 1982. An earlier, similar system was used under previous Radio Regulations. The bandwidth part (BBBB) uses four characters: three digits and one letter. The letter sits where a decimal point would normally go and shows the frequency unit. H means hertz, K means kilohertz, M means megahertz, and G means gigahertz. For example, "500H" stands for 500 Hz, and "2M50" means 2.5 MHz. The first character must be a digit from 1 to 9 or the letter H—it cannot be 0 or any other letter. The type of modulating signal used to have categories 4 and 5 for facsimile and video, but those were removed when the 1982 Radio Regulations came in. The type of transmitted information, details of that information, and multiplexing are all defined by the later characters in the label. Some signals can fit more than one label, so a transmission might be correctly described by two or more designators. In those cases, there is usually a preferred conventional one. Common examples include: - A3E or A3E G: ordinary amplitude modulation used for low-frequency and medium-frequency AM broadcasting. - A8E or A8E H: AM stereo broadcasting.
- Agreement year
- 1979
- Effective date
- 1 January 1982
- Governing body
- International Telecommunication Union
- Designation format
- BBBB 123 45
- Bandwidth units
- H (Hertz), K (kiloHertz), M (megaHertz), G (gigaHertz)
- Removed types
- Types 4 and 5 (facsimile and video) removed with 1982 Radio Regulations
Lore & Background
The ITU classification system was agreed at the 1979 World Administrative Radio Conference (WARC 79), giving 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 system is based on characteristics of the signal, not on the transmitter used, and uses a format of bandwidth followed by up to five fields: modulation type (letter), modulating signal type (digit), information type (letter), and optional details and multiplexing letters. Types 4 and 5 for modulating signal 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, though a preferred conventional designator usually exists.
Reader's Guide
The ITU emission designation system provides a standardized way to describe any radio frequency signal based on its technical characteristics, enabling unambiguous identification across international borders and services. Its significance lies in its adoption by the ITU, the global authority on radio communications, and its incorporation into the Radio Regulations that came into force on 1 January 1982. The system covers all types of emissions, from simple continuous wave (A1A) to complex digital television (C7W, G7W). Common examples include A3E for AM broadcasting, F8E for FM stereo broadcasting, J3E for SSB speech, and F1B for frequency-shift keying telegraphy. The bandwidth notation uses a letter as a decimal point (e.g., 2M50 for 2.5 MHz). The system's legacy is its continued use in regulatory and technical contexts worldwide, providing a consistent framework for describing emissions regardless of the transmitter hardware.
Did You Know?
- Bandwidth is expressed as four characters: three digits and one letter, where the letter indicates the unit (H, K, M, or G).
- FM stereo is designated F8E, not D8E, because the designation is based on the main carrier, not subcarriers.
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