Dispatch Simulcast on SD City TRS, 4688

[GroundLoop]

I was wondering if someone could explain the interesting operation of TGID 4688 on San Diego City TRS.
When they place a call, it looks like this:

There are three Adds, maybe a Drop, and a Call.
Some time later, there are Drops.

Some Drops don't have a Source or Target ID, others have a Target ID only.
What does an anonymous (no ID) drop do?

 

[inigo88]

What you're seeing is the dispatcher at Station F "Multi-Select" talkgroup 4688, Fire Admin 7A and Fire Dispatch 7B. They MSEL all three talkgroups for every dispatch, but the talkgroup your scanner stops on depends on the order in which they select them.

Interestingly enough there is a four digit DTMF tone out that precedes every dispatch, but it only goes out on talkgroup 4688. After the DTMF tone out the dispatcher MSELs the three talkgroups, the standard "beep beep beep" alert tones go out and then the dispatch. Following the dispatch the dispatcher "drops" the Multi-Select, which is what you're seeing at the end there.

It's been suggested on this forum in the past and scandiego that talkgroup 4688 is a fire dispatch simulcast channel meant for the San Diego Lifeguards, which would be consistent with the other Lifeguard talkgroups in the 4000 range.

 

[WayneH]

There could be some screwiness to how UniTrunker is interpreting the data. Announcements of patches and MSELs can be a pain to code for in software. There is an actual code to indicated the patch or MSEL has dropped a group or groups and then sometimes you won't see them. Then the frequency of the announcements varies so sometimes you don't know if a patch is valid or not. Typically once an MSEL call is done there should be a drop command but 3600 trunking can be odd like that sometimes.

 

[inigo88]

I found this old thread on scandiego which cleared up a lot of old questions. A couple points directly from a "Station F" SDFD dispatcher:

Actually 4688 is the Life Guard simulcast of SDFD dispatch.

We do use Multi-select through the Motorola consoles, but I don't think that would have anything to do with it...but what do I know. For about the last two years, the Dispatch position has been simulcasting all dispatches on the Station Alerting circuit, and the Admin and Dispatch TG's.

For scanners not capable of receiving patched talkgroups, it mentions in the thread that the dispatch talkgroup "SuperID" is the last of the three talkgroups multi-selected on the console screen. Each dispatcher has their own personal preference to the order in which they click the squares on the screen (in the case of a Motorola Centracom Elite console), which explains the variation in which talkgroup ultimately shows up as the SuperID for the dispatch.

Considering the Lifeguard SDFD Dispatch Simulcast talkgroup (4688) is the only one containing the preceding DTMF alert tones, that may mean it's a simulcast of the station alerting circuit (although I thought SDFD does station alerting with MOSCAD). Another case may be a backwards compatibility with Minitor pagers for the Lifeguards, although the DTMF tones precede every dispatch - not just those that would be applicable to the Lifeguards. Anyone know the answer?

 

[GroundLoop]

The tip about DTMF preceding the 5008 MSEL was very good.. Much nicer to monitor 5008 than 4688.

 

[WayneH]

DTMF is commonly used to activate tones at a Station.

 

[Anderegg]

I only listen to 4688......the tones are an indication of the seriousness of a dispatch......when you hear 4-6 tones, you can be prepared for a major incident dispatch.....the tones also give me a chance to turn down my other scanners and lets priority features work better giving more lead time so you dont miss the begining of a dispatch.

Paul