SDFD - Disp Simulcast vs Disp 7B

[Gamefreak88]

Can someone explain to me the difference between these two talkgroups? Would listening to only one or the other be a bad idea (e.g. missed radio traffic)?

Disp 7B (TGID 5008)
Disp Simulcast (TGID 4688)

I'd like to set up a scanner locked-in on San Diego FD dispatch.

Does one start before the other? (and yes, every second counts)
Does one pick up better throughout the county in general than the other?
Does one carry more radio traffic than the other?
Does one transmit special data ("tone outs"??) and the other doesnt?

I don't understand the difference.

 

[Gamefreak88]

Upon further research with these two threads, it would appear the answer I am looking for is Disp Simulcast (TGID 4688), based on the fact that it starts sooner due to the DTMF tone outs, which is incredibly useful for gauging the severity of a dispatch. For example, a medical aid will often have one set of beeps, whereas a structure fire or vehicle rescue could easily be 4 or more.

BUT, in my pursuit of knowledge, I must ask. What else is different besides the tone-outs on Disp Simulcast?

http://forums.radioreference.com/sa...88616-san-diego-fire-dispatch-talkgroups.html
http://forums.radioreference.com/sa...12-dispatch-simulcast-sd-city-trs-4688-a.html

 

[K6CDO]

4688 is the station alerting TG. It is not programmed into mobiles or portables.
5008 is the TG used by units in the field to receive the dispatch.

 

[JoeyC]

Always wondered about that. Listening to the two held talkgroups in separate scanners for the last hour, I have yet to hear anything come over 5008. Many dispatches over 4688 though.

 

[Gamefreak88]

It appears Disp Simulcast (TGID 4688) is better in all ways, with the only con being that some people don't want to hear the DTMF tone-outs. In my case I love the tone-outs. Gives me more time to grab my computer to write down an address.

K6CDO, interesting info! So one could essentially say one is "Fire Station Dispatch" and one is "Firefighter Dispatch".

 

[inigo88]

When a fire dispatch goes out, the dispatcher sometimes sends out DTMF pre-alert tones on 4688, presumably to activate the station alerting speaker at certain stations. With that complete, the dispatcher then multi-selects the station alert (4688), ADMIN 7A and DISPATCH 7B talkgroups. That's when you hear the "Beep beep beep" tone, followed by the voice dispatch. Multi-Select is a temporary dispatcher-initiated patch between talkgroups, and works on Motorola systems by taking multiple talkgroups and slaving them to one single talkgroup, called the "supergroup." So if you hear the voice dispatch on 4688, it's because the dispatcher multi-selected 7A, 7B and the station alerting talkgroup and 4688 was the "supergroup."

Any radio set to ADMIN 7A or DISPATCH 7B would get a message from the control channel, essentially saying "If you're monitoring 7A or 7B, automatically switch to talkgroup 4688 for the duration of the multi-select." When the dispatcher finishes talking and drops the multi-select, the three talkgroups become separate again. Hope that makes sense.

 

[WayneH]

Good explanation Inigo.

GRE has never picked up the idea of following patches but I think Uniden tried it. One problem is when you're scanning more than the system the feature is pretty much useless since the scanner needs to decode the patch/MSEL information before it gets the tagged call.

 

[zerg901]

I imagine that there is no need to send any alerts via TG 4688 if none of the required units are at home in their stations. In this case, if a scannerist was to just monitor TG4688, one could miss some incidents.

 

[inigo88]

Good explanation Inigo.

GRE has never picked up the idea of following patches but I think Uniden tried it. One problem is when you're scanning more than the system the feature is pretty much useless since the scanner needs to decode the patch/MSEL information before it gets the tagged call.

Believe it or not, my GRE PSR-500 does scan multi-selects and patches now, and will even priority scan talkgroups... but only for ANALOG motorola systems (because all these features use the subaudible data). I'm not sure if they fixed it with the PSR-800, but the -500 does not detect patches/MSELs or priority scan digital talkgroups, because those features rely on embedded P25 data packets and not simply analog subaudible data.

So in the case of the San Diego City system, which is still analog, I never miss a fire dispatch because if I'm holding on DISP 7B and the supergroup turns out to be ADMIN 7A or TG 4688, the scanner just automatically switches and says "Ptch" in the top left corner.

Of course, the first and best way to not miss any system activity is still to use control channel decoding software.