P25 Phase II Questions

[lisalolo]

What is the difference between the two phases? Will Phase I be phased out eventually and Phase II taken over?

Is the audio quality any difference in Phase II? Thanks!

[oemctx4]

Phase 1 support 25Khz/12.5Khz channel spacing. Phase 2 support the future spacing of 6.25khz.

[Unitrunker]

Originally Posted by lisalolo

What is the difference between the two phases?

Phase two allows two slot TDMA on a traffic channel. That's two independent conversations. The voice channels may be mixed Phase 1 compatible voice channels interleaved with Phase 2 channels. Control channels are essentially the same.

Will Phase I be phased out eventually and Phase II taken over?

Possibly. All Phase 1 radios would need to be upgraded or replaced.

For simplicity, interop and mutual aid channels might stay Phase 1.

[MattSR]

Originally Posted by oemctx4

Phase 1 support 25Khz/12.5Khz channel spacing. Phase 2 support the future spacing of 6.25khz.

Not quite - that was the sales message from Motorola and the TIA in the early 90's which was based on a dream that future advances in electronics would allow them to meet their targets inside a 6.25khz channel.

It seems that either the state of the art in electronics isn't what they expected, or the laws of physics intervened, so P25 Phase 2 is actually 6.25kHz "equivalent" meaning that 2 slot TDMA inside a 12.5kHz channel was require to meet the targets of phase 2.

A P25 Phase 2 channel still requires 12.5 kHz of RF bandwidth no matter how you look at it.

Cheers,
Matt

[Unitrunker]

Clock accuracy is a problem at 6.25 kHz.

A 600 Hz error at both ends at 12.5 kHz is tolerable. Not so at 6.25 kHz.

[brownlab]

Originally Posted by lisalolo

What is the difference between the two phases? Will Phase I be phased out eventually and Phase II taken over?

Is the audio quality any difference in Phase II? Thanks!

If you have not already, you may also want to read the posts below this one regarding Phase II mixed mode FDMA/TDMA. Don S provides an excellent explanation

[c1mf]

dont know much about p25 but are there any scanners that can recive p25 phase two in the market

[brownlab]

Originally Posted by c1mf

dont know much about p25 but are there any scanners that can recive p25 phase two in the market

No. The GRE PSR 800 can decode X-2 but not Phase 2 TDMA. Does the 800 have the correct hardware to decode Phase 2 TDMA via a frimware update? Right now that is the $400 question.

[c1mf]

thanks was considering buying a gre 800 but im not sure if i should wait for the 900 thats supposed to be coming out this year