Phase 2 systems using Phase 1?

[Progline]

Why would a Phase 2 system have Phase 1 transmissions? I was listening to LA-RICS on my P25P1 scanner the other day, and was surprised to hear a Phase 1 conversation. (The only time I've ever heard that). Are certain talkgroups assigned to use Phase 1, and the rest are the default (P2)? I can't imagine that phase type would be user-selectable, so it must be controlled by the system software at the talk-group level? I honestly never expected to hear a phase 1 transmission on LA-RICS.

 

[iMONITOR]

They want backward Phase 1 compatibility with those who haven't upgraded to Phase 2. This is beginning to happen in Michigan.

 

[GTR8000]

P25 systems can optionally be capable of dual-mode operation. The actual terminology varies by manufacturer, but essentially the system will prefer to operate in TDMA mode to maximize efficiency, however if an FDMA-only subscriber affiliates, the talkgroup can fall back to FDMA mode. This sort of setup was popular when Phase II was first being rolled out a decade ago, so that older radios that weren't capable of TDMA could still be used to ease the transition. Nowadays the trend is more towards strapping all talkgroups for TDMA only, but dual mode is still a thing. By the way, it's determined at the talkgroup level, at least for Motorola ASTRO 25 systems. FDMA only, TDMA only, or FDMA/TDMA DDM (Dynamic Dual Mode)

 

[pewpew45]

There are still a handful (More then a handful) of mobile XTL5000 in sheriff units. Thus the talk groups capable and enabled for phase 1 also.. As the cars get swapped out or they get more APX8500 mobiles that will eliminate the phase 1 need.