Tdma - fdma

737mech · #1 (**permalink**) 10-26-2012, 6:01 PM

Ok so to be clear The PSR500 cannot decode x2TDMA? It might be possible that a RRDB entry for this system was incorrect? Southern Nevada Area Communications Council (SNACC-Project 25) System Trunking System, Las Vegas, Multi-State - Scanner Frequencies I ran unitrunker on it and got info, I should not be able to do that if this was x2TDMA correct? The unitrunker also labels it FDMA? I just got pro96com working today, where does it show FDMA or TDMA?

Jay911 · #2 (**permalink**) 10-26-2012, 6:40 PM

Running Unitrunker is not the same as decoding voice. Unitrunker listens to the control channel on the system, which is always (at current time) FDMA. It will even show you TDMA channels.

It's tuning/decoding voice in TDMA mode that you need a PSR800 for.

fourthhorseman · #3 (**permalink**) 10-26-2012, 6:45 PM

the 800 can decode both X2/moto flavor and phase 2.the recent updates suggest.

Chauffeur6 · #4 (**permalink**) 10-26-2012, 6:53 PM

Run Unitrunker on the control channel, then look at the Info tab of the Site window...what does is say for Channel Access? FDMA = Phase I, X2 = X2-TDMA and P2 = Phase II

No scanner except for the PSR-800 can decode any form of TDMA. That applies to decoding the voice channels, it has nothing to do with the control channel data, which is what Unitrunker and Pro96Com monitor.

Also, just because a system is in the RRDB as X2-TDMA or Phase II, that doesn't necessarily mean that every talkgroup is using TDMA. There may be some FDMA talkgroups which any digital scanner that supports P25 can decode.

737mech · #5 (**permalink**) 10-26-2012, 7:12 PM

Quote:

Originally Posted by Chauffeur6

Run Unitrunker on the control channel, then look at the Info tab of the Site window...what does is say for Channel Access? P1 = Phase I, X2 = X2-TDMA and P2 = Phase II

No scanner except for the PSR-800 can decode any form of TDMA. That applies to decoding the voice channels, it has nothing to do with the control channel data, which is what Unitrunker and Pro96Com monitor.

Also, just because a system is in the RRDB as X2-TDMA or Phase II, that doesn't necessarily mean that every talkgroup is using TDMA. There may be some FDMA talkgroups which any digital scanner that supports P25 can decode.

Ok so if I had a PSR800 I should be able to actually hear unencrypted voice channels on this system? Or is the "decode" the key word here? Decode with what?

As I posted the unitrunker system info tab says channel access FDMA.

Chauffeur6 · #6 (**permalink**) 10-26-2012, 7:21 PM

The PSR-800 can "hear" X2-TDMA and Phase II TDMA (with the beta firmware that was just released) non-encrypted voice, yes.

If Unitrunker shows "FDMA" for the channel access, then the system is Phase I, not X2-TDMA or Phase II.

Are you able to decode both sites with Unitrunker? If yes, same results on both?

mikey60 · #7 (**permalink**) 10-26-2012, 8:21 PM

Quote:

Originally Posted by 737mech

I just got pro96com working today, where does it show FDMA or TDMA?

Pro96Com will show the frequency with a slot number (/0 or /1) when a talkgroup is using a TDMA channel. If there's no slot number, then the talkgroup is using a FDMA channel.

Mike

mikev · #8 (**permalink**) 10-27-2012, 3:38 PM

Quote:

Originally Posted by mikey60

Pro96Com will show the frequency with a slot number (/0 or /1) when a talkgroup is using a TDMA channel. If there's no slot number, then the talkgroup is using a FDMA channel.

And this is exactly how it should be phrased.

Talkgroups are not TDMA or FDMA. Channels are TDMA or FDMA. When someone presses the Talk button on their radio, their talkgroup is assigned to a channel based on the capabilities of all the radios affiliated to that talkgroup.

If all radios within an agency are all TDMA-capable, then the talkgroup(s) for that agency will most likely always be on a TDMA channel. But that does not mean that the talkgroup(s) for that agency are TDMA.

For example, here in Loudoun County, VA ... Town of Leesburg Police transmissions are always on TDMA channels (smaller force, all radios should be TDMA capable). But at times, one or both of the Sheriff's Office Dispatch talkgroups will go back and forth between TDMA and FDMA channels. Fire and Rescue dispatch is almost always on FDMA channels, while the Response talkgroup goes back and forth between TDMA and FDMA channels.

Chauffeur6 · #9 (**permalink**) 10-27-2012, 4:22 PM

Quote:

Originally Posted by mikev

And this is exactly how it should be phrased.

Talkgroups are not TDMA or FDMA.

Not quite. Each talkgroup is established in the zone controller as to what capability is has: FDMA-only, TDMA-only or DDM (Dynamic Dual Mode). DDM is an option which allows talkgroups to switch mode on-the-fly depending on the capabilities of the subscribers units that are affiliated with that talkgroup at any given time. This is where your Loudoun County examples of seeing shifting FDMA/TDMA talkgroups comes into play. Not all systems are spec'd with the DDM option, which means there are X2/P2 systems that will only have FDMA-only or TDMA-only talkgroups, but cannot have mixed-mode talkgroups.

Remember, TDMA talkgroups use the same frequencies as FDMA talkgroups, they simply divide the channel into two "slots", whereas an FDMA talkgroup uses the full bandwidth of the frequency, i.e. "both slots at once". However, the talkgroups themselves must first be designated as noted above.

So fundamentally, it is indeed the talkgroup that determines whether FDMA, TDMA or mixed-mode is to be used. Only at that point do the channels (slots) that are assigned come into play.