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Trunk Track Different Talkgroups Simultaneously?

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phenoman

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Hey. I've not bought a scanner as yet but one thing about trunk tracking puzzles me. Here's my view of how it works (a Motorola Type 2 system):

Someone hits PTT. His radio transmits a request to the control computer. The computer responds with an available channel number on the control channel. The requesting radio shifts in frequency to the designated channel, along with all other radios in the talkgroup. The initiator proceeds to transmit on the frequency and is heard by everyone tuned in. When he finishes transmitting, the channel is open and all the radios in the talkgroup return to monitoring the control channel.

Now, what puzzles me is from a scanning perspective. Suppose I'm trunk tracking with any Uniden scanner. I'm monitoring the control channel in control chan only mode. After the control computer assigns a temporary frequency to the talkgroup, my radio automatically shifts to monitoring the channel and I hear the transmitter talking to those in his group.

What happens if another user in a different talkgroup decides to request a channel during the time I am listening to the first group? Since I am not watching the control channel, am I completely oblivious to this fact and will miss the entire transmission of the second group?

(I'm sorry this is getting long.)

For example, suppose I want to monitor the Fort Lauderdale PD,
http://www.radioreference.com/modules.php?name=TRSDB&sid=217
on talkgroups 17680, 17712 and 17744. If a member of one of those groups requests a channel while I am listening to another group, will I miss the second group's communication entirely?

Ok, that's it. Thanks for reading all of that, I like to be clear (if not concise :)
 

rdale

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Correct, just as the person listening to that talkgroup with a regular radio (non-scanner) will also miss.

- Rob
 

UPMan

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The TG Channel assignments are repeated, so even if you miss the first of the conversation (as would happen if you were off listening to another TG at the time), when the scanner returns to the control channel, it will see the TG activity on the next update. I believe how often these repeats happen depend on how the system is set up and how busy the system is (i.e. the system updates more often when fewer TG's are active).
 

phenoman

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So the control channel carries info on all talkgroups in use as long as the channel is open? Fantastic! This means I'll be able to cut short of monitoring one TG if I want to get back to watching the control channel.

Thanks Fellas!
 

SCPD

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If you need to monitor two TGs in a way that gives one priority over the other, you will need two radios (non-trunked, one computer controlled) and a program like trunker. One of the radios monitors the CC full time. When the software sees a higher priority TG, it commands the second radio to tune to more important conversation.

If you actually want to hear more than one conversation at once (rare but some folks actually need this), you can configure a program like T4Win with three (or more) radios. Two of the radios must be computer controlled and the computer must have enough ports to connect to them.

-rick
 

JoeyC

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The scanner monitors the control channel at all times whether or not the radio is currently tuned to the freq carrying the conversation on TG 17120. When you hold on 17120 thats all you're going to hear. No different than if you had the scanner held conventionally on 154.16. If you want to hear TG 1616 at all costs even when your radio is receiving 17120, the simple thing to do, get a 2nd scanner. You almost need multiple scanners in a trunking environment if you want to monitor multiple TGs and "can't miss" activity on certain ones. In the days of conventional only scanning, I got away with one scanner. Now that just about everything I like to listen to is trunked, I've got 4 going, 6 when something really big is going on.
 

rdale

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"The scanner monitors the control channel at all times whether or not the radio is currently tuned to the freq carrying the conversation on TG 17120."

Incorrect - that would require two receivers inside the scanner. It monitors the control channel a talkgroup becomes active then it switches to the freq the talkgroup uses (so you hear the conversation) and when it's done or when you hit SCAN it goes back to the CC.
 

INDY72

Monitoring since 1982, using radios since 1991.
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Sorta simple fix....
If your only say watching a couple of TG's, set the one you really need as PRIORITY TG! then while your monitoring the others, then if any convo happens on the PRIORITY TG you will hear it.
 

Thornhill20

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rdale said:
Incorrect - that would require two receivers inside the scanner. It monitors the control channel a talkgroup becomes active then it switches to the freq the talkgroup uses (so you hear the conversation) and when it's done or when you hit SCAN it goes back to the CC.

That isn't totally wrong.

Motorola trunking systems transmit low-speed trunking data on the voice channels, so the radio can still monitor the control channel while receiving a voice call.

Listen to your scanner with a pair of good headphones - you'll hear what I mean.

-Mike
 

rdale

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"Motorola trunking systems transmit low-speed trunking data on the voice"

Not 9600 baud digital systems, and none of the Uniden models ever utilized it (as I recall just the very early and problematic RS line?) As for talkgroup priority - I know that the Pro96 doesn't have it - which Uniden models offer that?

- Rob
 

JoeyC

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rdale said:
"The scanner monitors the control channel at all times whether or not the radio is currently tuned to the freq carrying the conversation on TG 17120."

Incorrect - that would require two receivers inside the scanner. It monitors the control channel a talkgroup becomes active then it switches to the freq the talkgroup uses (so you hear the conversation) and when it's done or when you hit SCAN it goes back to the CC.

You are correct, I mispoke. The point of the guys inquiry (I believe) was whether he was going to "miss" traffic on a specific talkgroup while monitoring another.

Using talkgroup priority is ineffective as it only "prioritizes" while listening to the control channel. If the scanner is listening to 17120 and 1616 (set as priority talkgroup) goes active also, the scanner isn't going to move to 1616 until the 17120 activity ceases. In conventional scanning, priority channels are sampled every second or so. This does not occur within the talkgroups while trunk scanning.
 

INDY72

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Not sure about the NEW unidens, but on the PRO-2052, the priority TG is priority scanned every two seconds just like priority feature on conventional. In fact all the trunkers that I have seen that have a priority tg scan work the same. If you have the TG priority feature turned on, then no matter what tg your listening to, if traffic comes over the priority tg, then it will kick over to that tg. Anyone got info on this feature on the Unidens????
 

waynesewell

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From the bc296d manual:

Code:
Setting Priority Talkgroups (Motorola and EDACS only) 

Talkgroup priority works slightly different than conventional priority. With talkgroup priority, the priority talkgroups are only checked when the scanner is on the control channel. So, if you have delay turned on for the system or are holding on an ID, the scanner will immediately switch to the priority talkgroup if it becomes active during the 2-second delay or while there is no transmission on the held talkgroup. To assign a talkgroup as the priority talkgroup, select it in Scan Hold mode (see “Holding on a Single Talkgroup”). Then, press and hold PRI for 2 seconds.
 

JoeyC

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milf said:
Not sure about the NEW unidens, but on the PRO-2052, the priority TG is priority scanned every two seconds just like priority feature on conventional. In fact all the trunkers that I have seen that have a priority tg scan work the same. If you have the TG priority feature turned on, then no matter what tg your listening to, if traffic comes over the priority tg, then it will kick over to that tg. Anyone got info on this feature on the Unidens????

My bad, I was talking about the newer Unidens.
 

INDY72

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So pretty much have to have at least two trunkers running. OK.... that can get expensive especially if your tracking a digital system. But as has been siad many times, a die hard scannist will pay out the wazoo to listen to what he wants.
 
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