I believe wherever you read that says it’s both phase I & II is referring to the phase II system having a backwards capability with phase I systems… a nice selling point when talking about upgrading statewide or regional systems, actually very large systems to TDMA (digital-which is believed to have measurable increased performance parameters) from FDMA, (analogue). A quick explanation of how the agency can jump from the old to the new was explained to me as this; Once it’s determined an agency is moving to TDMA the new phase II backbone equipment gets installed at the dispatch and site locations right next to the older phase I equipment which is left in service until the last FDMA radio is gone. Then the swap out of all the vehicle radios begins. That may take some time. There may be manufacturing constraints where they can only supply x amount of radios at a time. Or, the agency may have budgetary constraints on how many radios the yearly budget will support, so it’s done over a period of years. The vehicle install process can take months to complete. Having a new radio system that will allow the old system to perform in the interim while all the time allowing comms between the two is a very big advantage. The process should be transparent to a dispatcher (other than the noticeable audible differences between FDMA & TDMA. I believe the TDMA audio can get compressed.)
This description of how the transitioning process works is general in nature. I’m sure there are those who know better than I. Please correct that which you believe I have gotten in error.
You got a lot wrong there, unfortunately.
First of all, FDMA and TDMA are both digital when we're talking about P25. All P25 is all digital, all the time, no exceptions. I find it a bit odd that you state FDMA = analog. Not in the sense we're talking about here, no.
Secondly, TDMA doesn't require "separate equipment installation alongside the older Phase I equipment" If a P25 FDMA system is already in place, and as long as the repeaters are capable of TDMA (which nearly all modern P25 repeaters are), it's a fairly simple and straightforward software upgrade to enable TDMA functionality. Same for the subscribers. As long as the hardware is TDMA capable, you pay whatever licensing fees there are for the new functionality, and you software/firmware upgrade existing repeaters and subscribers to provision that capability.
In any event, the CLMRN is a Phase II system with the majority of talkgroups operating in TDMA mode. While the system itself is capable of "falling back" to Phase I FDMA mode, it's likely that this ability is disabled on most of the talkgroups in order to ensure maximum efficiency. As long as every subscriber in a fleet is TDMA capable, and those talkgroups are exclusive to that agency and aren't used for mutual aid/interop purposes, then there is no reason for FDMA to be allowed, as it wastes precious RF resources.
