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P25 Question

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rbrtklamp2

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To my knowledge there are 4 types of P25 modulation C4FM, CQPSK, WIDE, and the new Phase 2 TDMA. My question is when are these P25 settings used, for example I know CQPSK is used on simulcast 9600 Baud 100% P25 trunked systems especially when narrow banded, but is it also used on conventional P25 Simulcast repeaters or is all conventional P25 C4FM? Basically what I would like to know is what circumstances determine what modulation is used on a P25 signal whether it is trunked or conventional? Also is there any conventional use of P25 Phase 2 or is that limited to trunking applications only?

Thank you for any answers,
Robert Klamp
 
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SCPD

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For phase 1, the mobiles and handhelds transmit C4FM. The repeater (trunked or not) may transmit C4FM or CQPSK for simulcast.

The phase 2 waveform is the same for single site and simulcast.

I don't think phase 2 is limited to trunking but can't say for sure.

Note that the control channel is always either of the two phase 1 waveforms.

I have no idea what "wide" is as a P25 modulation.
 

MattSR

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WIDE comes from the era of Motorola ASTRO gear that was IMBE CAI compatible (post 1996) but still pre P25 compliant (prior to 2002-2003 or so)

WIDE is C4FM with modified deviation, symbol parameters and Nyquist ISI/RRC filtering that made use of the FM capture effect to make simulcast work better. It also requires a 25khz wide channel - hence the name.

Wide was replaced in P25 Phase 1 with CQPSK LSM style modulation, since its far more spectrally efficient and fits in a 12.5khz channel.

Cheers,
Matt
 
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