BG2EFX 5kHz 的音频再怎么 FM 也调制不出来 25 kHz 的带宽
Narrow Band FM - Land Mobile Radio Above 150 MHz
In the United States, the FCC requires Part 90 land mobile (business radio, as well as public safety radio systems) operating above 150 MHz must use narrow band frequency modulation narrowband FM deviation (2.5 kHz deviation, 11.25 kHz bandwidth limit). This requirement went into effect in 2013 and is commonly known as the FCC narrowbanding mandate. Land mobile radios (Motorola, etc.) should be set to "12.5 kHz channel spacing" or "12.5 kHz channel" mode for narrow mode.
Other radios call this "12K" mode or simply "NARR" or "NARROW". Computer programming settings generally require switching the radio to NFM mode for narrowband FM (vs. FM mode for regular 4/5 kHz bandwidth). Land mobile licenses must reflect the use of the narrowband emission designator - 11K3F3E, 11K2F3E, 11K0F3E are all considered identical in the eyes of the FCC. Another example would be Alinco radios, which use 8.5 kHz bandwidth narrow band FM for narrow mode - emission: 8K50F3E and 16 kHz bandwidth for regular wide mode - emission: 16K0F3E. Baofeng, etc. radios such as the UV-5R, UV-82, UV-25 and so on have a "WIDE" and "NARR" setting available, NARROW being narrow band FM, 9K20F3E or 9K10F3E emission depending on the source.
The Part 95 license free Family Radio Service (FRS) also uses narrow for all 22 channels in simplex mode. FRS shares all 22 of its frequencies with the GMRS service.
GMRS, regular "wide" deviation (4 kHz - 5 kHz deviation) is allowed on channels 15-22 (in simplex mode and as part of GMRS repeaters). Narrow mode is required on 3 of the 5 license free MURS channels on the VHF band. 4 kHz deviation is generally identified as "20 kHz bandwidth" or "20 kHz channel" with emission designator 16K0F3E or 16K0G3E on VHF marine, 5 kHz is called "25 kHz bandwidth" with emission designator 20K0F3E. In practice, 4 kHz and 5 kHz deviation are interchangeable with each other, however the wider deviation signal will sound louder on most receivers, and may cause distortion if the receiver is configured in the narrowband mode.
Amateur radio and the VHF marine band are exempt from this requirement, as are services operating below 150 MHz (for land mobile, that means the 25 MHz - 50 MHz VHF low band and 72-76 MHz VHF mid band). Outside the U.S., use of narrow deviation is commonplace even on VHF low band.
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