"Simplex" Talkgroups?

[PhillyPhoto]

Philly PD has a talkgroup for citywide announcements of shootings, robberies, etc. Every now and then, when getting information on an important enough event (like tonight, there was a police-involved shooting) "J-Band" as it is known, will talk to the districts, or certain units to get information from them. I heard J-band talking and requesting information, and then dead air, and then them talking again continuing to the next question.

My question is, is there anyway to setup a talkgroup so only the dispatcher can hear it? The only other thing I can think of is that the talking unit is encrypted for some reason.

BTW, Philly uses a 3600bps/baud SmartZone system.

[Twisted_Pear]

From what I recall of SZ features is that a console operator can disable re-transmit so that the mobile never comes out the system outbound side. Personally, I've never seen it done so I'm not exactly sure how the system reacts to that mode.

[N4DES]

That is a viable option and programmed as a console feature.

We tried to use it to simulate a "transit system" on our TRS for the public transportation fleet, and honestly
it didn't work very well. We ended up re-programming the bus radios to allow private calls. We found using PC
easier to manage and the dispatchers feel like they have more control of the conversation.

[MikeOxlong]

Almost sounds like a Multiselect.

Radios that don't need to listen to the routine traffic can sit on the announcement group and only hear the important stuff.

The dispatcher can multiselect the appropriate dispatch groups and the announcement group and make the announcement.

If you're listening to the announcement group and somebody responds on a dispatch group, you'll probably never hear them.

[mr.syntrx]

You get that all the time around here. The operator will often multiselect about five or more different groups, usually because they've left all those groups selected after their daily weather/fire hazard broadcast, and you have to keep searching through these groups to figure out where the conversation is taking place.

[PhillyPhoto]

Almost sounds like a Multiselect.

Radios that don't need to listen to the routine traffic can sit on the announcement group and only hear the important stuff.

The dispatcher can multiselect the appropriate dispatch groups and the announcement group and make the announcement.

If you're listening to the announcement group and somebody responds on a dispatch group, you'll probably never hear them.

Now that I think about it, this might be closer to what's happening. On the fire side, often times they will dispatch on two different bands to make sure a unit heres them. For instance, when dispatching a fire close to the middle part of the city, they will dispatch on both North Fire and South Fire bands, and when dispatching a medic unit, they will dispatch on the appropriate medic and fire band (North Medic / North Fire).