Determine Talkgroup from Mobile Radio?

Dave_D · #1 (**permalink**) 04-08-2008, 06:03 PM

Hi all,

I love my trunk-tracking scanner, but when I scan input frequencies, it won't display the mobile radio's talkgroup information. I've since learned that mobile radios communicate to the site controller over a dedicated control channel input frequency. Certainly, the mobile radio transmits its group ID to the site controller when requesting a channel pair, no?

Could a new generation of trunk-tracking scanners monitor the system's control channel input frequency to determine the mobile radio's (input frequency's) group?

On the other hand, would it be possible to determine a mobile radio's (input frequency's) group by decoding the control channel output frequency's response to the mobile's request for a channel pair?

Dave

JoeyC · #2 (**permalink**) 04-08-2008, 06:26 PM

Why would you want to monitor input freqs on a trunked system?

Dave_D · #3 (**permalink**) 04-08-2008, 07:34 PM

I want to restrict my scanning to nearby activities.

JoeyC · #4 (**permalink**) 04-08-2008, 10:38 PM

If I understand you correctly, you want to trunktrack by input freqs.

To restrict scanning to nearby activities alls you have to do is scan the inputs. You don't need a trunk tracking scanner for that. You will never see a trunk tracking scanner that trunks based on input signals by talkgroup. I can't see any practical reason why anyone would want this in a trunking scanner except for shady purposes. And its probably not possible anyway.

wayne_h · #5 (**permalink**) 04-08-2008, 11:05 PM

You would never hear the dispatcher either. This really makes no sense. If a dispatcher tells a unit to go to X address you would never even know where the unit is going unless he/she says so.

Dave_D · #6 (**permalink**) 04-09-2008, 01:19 AM

When listening to a trunked system, I can lockout all of the unwanted groups, thanks to trunk tracking. However, when monitoring input frequencies, there's no trunk tracking to identify the source or to lockout unwanted frequencies.

What I do now is listen to input frequencies (blindly) and then, when something of interest pops up, I might briefly enable output frequencies, just long enough to hear what's going on. The point is that I want to monitor things in my neighborhood without bombardment from the city.

BoxAlarm187 · #7 (**permalink**) 04-09-2008, 01:32 AM

Like the others, I don't understand the logic behind this either. If you're listening to the input side, you have no control over what you're going to hear on a trunked system - the nearby police, fire, EMS, public works, school buses, or anyone else that's accessing the system near you. This seems to ultimately defeat what you're trying to accomplish - unless you want to hear everything going on nearby, no matter what agency it is.

Unless you live in a really small city, why wouldn't you just listen to the beat/sector/whatever your PD calls it that covers the area where you live? This by monitoring this talkgroup, it would eliminate the need to listen to all of the other areas.

Since you're not hearing the dispatcher on the input side of the repeater, what are you hearing from the units in the field that's making your interested enough to listen to the output?

mancow · #8 (**permalink**) 04-09-2008, 01:39 AM

Actually, I think his idea makes perfect sense. It would be a neat tool for sleuthing. If a receiver could be set to CC mode and was able to snarf out the ISWs from a nearby transmission you could see what that specific unit was up to. It sounds similar to the old programs that used to sniff cellular mobile traffic to grab ESNs etc...

Dave_D · #9 (**permalink**) 04-09-2008, 01:57 AM

Quote:

Originally Posted by BoxAlarm187

If you're listening to the input side, you have no control over what you're going to hear on a trunked system - the nearby police, fire, EMS, public works, school buses, or anyone else that's accessing the system near you. This seems to ultimately defeat what you're trying to accomplish - unless you want to hear everything going on nearby, no matter what agency it is.

But that's just it. As explained in my prior post, I want to monitor nearby transmissions but lockout certain agencies. I do not want to monitor everything. This is all about filtering out unwanted transmissions; those from unwanted agencies and those from unwanted distances.

Quote:

Originally Posted by BoxAlarm187

Unless you live in a really small city, why wouldn't you just listen to the beat/sector/whatever your PD calls it that covers the area where you live? This by monitoring this talkgroup, it would eliminate the need to listen to all of the other areas.

Maybe I'm being too sensitive, but it's still too much. I don't care about the homicidal maniac 20 miles away. I do care about the homicidal maniac in my neighborhood. And it's rarely so interesting. When I listen to those talkgroups, it's a regular stream of banal chatter. [Granted, the nearby stuff is typically banal too, but that's a good thing.] It'd be really cool if my scanner would stay silent until such time, and then display the agency info and perhaps open up the respective repeater output channel.

Does this not make any sense? Maybe my geography is unique....

BoxAlarm187 · #10 (**permalink**) 04-09-2008, 02:04 AM

Quote:

Originally Posted by Dave_D

Does this not make any sense? Maybe my geography is unique....

Sure, it makes sense, it's just a highly unusual approach to scanning. I can see where your desire would be to only hear things within a mile of your house, but I just don't think you're going to find a way to make this happen by trying to get the TG's to associate with the inputs.

Good luck, I await to hear the response from others on this topic...

rescue161 · #11 (**permalink**) 04-09-2008, 05:51 AM

I used this same tecnique long before trunking scanners came into play. It worked out quire well for us because we only wanted to hear traffic near us. It did bother the crap out of me not to be able to follow conversations though.

I was in heaven when the Uniden 235 came out.

ayaresr · #12 (**permalink**) 04-09-2008, 06:10 PM

I too feel that the logic behind this doesn't make total sense. I can understand only wanting to monitor certain areas, and on some systems, I guess thats not always easy to do. The only time I have found listening to the repeater input useful was when the field unit had better signal to my location than the tower. And yes, lots of info was missed scanning that way.

randyK · #13 (**permalink**) 04-09-2008, 09:47 PM

I have one bank programmed for that purpose. I put the input freq, then the output freq, the next input, then the next output & so on. Then I have the outputs locked out. That way you can hit manual twice & listen to the output side. When the repeater drops, hit scan. This works well with the pro95 & 96 because you can set the output channel to motorola mode & it will display the TGID# when on the output freq. At least it will on a motorola system that uses priority monitor. Randy