P25 Phase 2 system

[wsmoore]

Does anybody know on a P25 Phase 2 System can an agency run TDMA ENC on 1 slot and run TDMA that reverts back to Phase 1 on another slot are is it one way for the whole system as far as reverting back to Phase 1?

Thanks, Shep Moore

 

[GTR8000]

Well for starters, Phase I is FDMA and so slots do not apply. An FDMA (Phase I) talkgroup uses the entire bandwidth of the frequency, and thus no TDMA (Phase II) activity is possible on that frequency for the duration of the FDMA transmission.

Generally speaking, FDMA and TDMA are per-talkgroup, not per-system. If there are enough traffic channels at the site, there can be a mix of FDMA and TDMA talkgroup activity, with the caveat explained above that FDMA takes up the whole frequency with a single transmission (less efficient), while TDMA alternates the transmissions in time slots, thus allowing two transmissions per frequency (more efficient).

Oh and encryption really has no bearing on anything. Either the talkgroup is clear or encrypted, FDMA or TDMA...still has to follow the above rules.

 

[MTS2000des]

Motorola Astro 25 systems support DDM, Dual Dynamic Mode, which allows a talkgroup to be provisioned for both TDMA and FDMA use. An FDMA only radio when affiliated to a DDM talkgroup, will downgrade the talkgroup to FDMA- even if it's only "listening". When the radio de-affiliates from the talkgroup, the talkgroup then reverts to TDMA.

Encryption is agnostic to FDMA/TDMA operation and is dependent on the programmed subscriber and the provisioning record allowing coded calls on both the talkgroup and the subscriber security capabilities profile.

 

[GTR8000]

PS - For the purposes of RRDB administration...flag talkgroups that have any TDMA usage observed to TDMA (T) mode (or TE/Te as appropriate). That flag is intended to indicate that a talkgroup is TDMA capable, not necessarily that it is full-time TDMA.

As @MTS2000des points out, ASTRO 25 systems optioned with Dynamic Dual Mode (DDM) allow talkgroups to switch between FDMA and TDMA on the fly, so it's important that any system in the RRDB with those sort of talkgroups be flagged as TDMA capable.