Business VHF and UHF

This is where working radio lives, and where the identities matter more than the audio. DMR, P25 and NXDN all name the caller and the group in clear even where the speech is encrypted, so the shape of a fleet is readable from the metadata alone.

Analogue channels give up their own identities too: the MDC-1200 burst when a Motorola key goes down, the DTMF unit number, and the CTCSS tone or DCS code that says which group a radio belongs to. Paging shares the same bands, and a fire pager toned out by a two-tone pair is the alert that precedes the voice dispatch.

$ waveshark --tune 453.5 --span 2400 --calls

What lives here

• POCSAG pagingPager messages in clear at 512, 1200 and 2400 bit/s, deduplicated because a paging network sends every page twice.
• FLEX pagingThe faster paging standard, at 1600 and 3200 baud in two and four level, read into the same message list as POCSAG.
• Two-tone pagingThe pair of tones that opens a fire or ambulance pager, named from an operator list so a call reads as a station rather than two frequencies.
• MDC-1200The burst a Motorola radio sends when its key goes down, naming the unit, so an analogue channel gains who as well as what.
• DMRWho called whom on which talkgroup, on both time slots, with speech through a source build carrying the ambe feature.
• P25 phase 1The talkgroup, the radio id and the key a call is under, off the C4FM frames North American public safety runs on.
• NXDNThe system number, who called whom, whether the call is enciphered, and the speech where it is not.