What is an emission?
An emission is the radio-frequency energy produced by a transmitter. The emission includes the carrier and any sidebands or other components needed to convey information.
Why emissions are classified
A standard emission designator describes the necessary bandwidth and the main characteristics of a signal. It allows regulators and operators to identify the type of transmission without a long technical description.
Three-symbol emission code
The basic emission designator uses three symbols after the necessary bandwidth. The first symbol describes the modulation of the main carrier. The second describes the nature of the signal modulating the carrier. The third describes the type of information transmitted.
First symbol: modulation
The first symbol identifies the main carrier modulation. Common examples include A for double-sideband amplitude modulation, J for single-sideband suppressed-carrier, F for frequency modulation and G for phase modulation. The full ITU table contains other symbols.
Second symbol: signal nature
The second symbol tells whether the modulating signal is a single channel or multiple channels, and whether it is digital or analogue. It helps distinguish a single digital channel from a single analogue channel.
Third symbol: information type
The third symbol describes the information sent. Examples include telegraphy intended for aural reception, telephony, facsimile, television, data transmission and combinations of information types.
Necessary bandwidth
Necessary bandwidth is the width of the frequency band needed for the required quality of transmission under specified conditions. It is not always the same as the total unwanted spectrum produced by a poorly adjusted transmitter.
Bandwidth notation
The necessary bandwidth is written before the three-symbol emission code. It uses letters and numerals under the ITU format. For example, 2K80J3E is a commonly encountered style of designator for a single-sideband telephony emission with a 2.80 kHz necessary bandwidth. Always confirm the exact designator in the relevant technical table.
Examples of emission types
AM, FM, SSB, CW, facsimile and data modes use different emission characteristics. The exact designator depends on the waveform and information type, not merely the name used by an operator.
Why correct emission matters
The emission must be one permitted for the operator's ASOC category and the band in use. A mode being technically possible on a radio does not mean it is legally permitted on every amateur band.