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P25 on the bands

Posted: 20 May 2020, 23:05
by 26mb04
Is there any P25 activity on the bands? There are/were some P25 capable repeaters, but info seems to be scarce. What codec is the norm, VSELP, IMBE or AMBE? Is the ID system the same as DMR? What about network access codes? It seems 295 is common for repeater access in USA.

Re: P25 on the bands

Posted: 28 May 2020, 10:45
by pete_uk
Its really an American thing, I doubt there are many radios in the hands of amateurs over here.

Phase 1 radio systems operate in 12.5 kHz digital mode using FDMA access method. Phase 1 radios use Continuous 4 level FM (C4FM) modulation—a special type of 4FSK modulation

To improve spectrum use, P25 Phase 2 was developed for trunking systems using a 2-slot TDMA. Phase 2 uses the AMBE+2 voice codec to reduce the needed bitrate so that one voice channel will only require 6,000 bits per second.

Re: P25 on the bands

Posted: 29 May 2020, 15:53
by 26mb04
That's fair enough, I knew it was largely a USA thing. I'm going to propose a UK P25-specific schedule for 70cm:

NAC: TX 293 (default), RX either 293 or F7E (all).
Talkgroup: 1 (default) , calling on FFFF (all)

Frequencies: Ideally the UK digital voice allocation for calling etc., but if it's busy with DMR go to 438.0375 and work up from there.