Isolating Astro Talkgroups

[DEMCERT14]

Hi all... I am trying to monitor an Astro Trunking System.

BACKGROUND
Currently I've got all the frequencies of the system programmed into my XTS2500i in conventional mode. The problem is, this system is 100% digital and trunking system has BOTH Clear and Encrypted talkgroups. All the voice traffic in Astro Clear is recieved fine by my XTS2500i on a conventional channel, however the Astro Encrypted is still all scrambled. Yes, I know that is to be expected of an encrypted signal.

CHALLENGE
Is there a way to program my XTS2500i (in conventional mode) to only unmute/recieve one particular talkgroup (Astro Clear Talkgroup) from the trunking system?

[RKG]

If your question is whether you can program a conventional radio to read the OSWs and follow channel assignments addressed to one particular talkgroup, then answer is no.

[nmfire10]

You're out of luck. The only thing that will do what you want is a trunk tracking scanner.

[GEMOTO]

I think what he is trying to do is make the ASTRO talk group determine if the receiver will unmute or not. Basically using the ASTRO talk group as a form of coded squelch.

Say he is on 855.2375 and wants to only hear talk group ID: 1234 on that particular frequency and no other voice traffic, regardless of the fact that he may only hear some of the conversation on that one frequency.

DEMCERT14, is this what you are trying to accomplish?

[DEMCERT14]

Hi GEMOTO, yes something similar. I'm trying to monitor my local federal government p25 trunking system. More info can be found here... http://www.radioreference.com/apps/db/?sid=5674 I am only focusing on one site, site 101, which consists of these frequencies: 406.26250, 406.83750 (CC), 407.23750, 408.26250, 409.10000, 409.66250, 409.76250, and 410.46250. Currently I've got all those frequencies programmed into my XTS2500i in conventional mode (except for the control channel freq). I've got the basic digital settings done correctly as I currently hear any and all unencrypted P25 digital transmissions on the frequencies. What I am trying to do is to only isolate Talkgroup 1097 so that I will only hear radio traffic from Talkgroup 1097 and ignore all other talkgroup transmissions over all the other programmed conventional frequencies. Any way this can be done? I was trying to mess around with the Talkgroup settings for Astro... but it wasn't really working out right for me.

[515]

You should be able to pick and choose which TG's you want to listen to with an XTS... You'll have to know the NAC (Network ID) that used on the voice channels, though.

First, under Conventional, ASTRO Systems, Astro Talkgroup list, create your list of TG's. You'll have to enter these TG's in decimal format, as opposed to hex in the trunking section.

Then, program all the voice channels in as ASTRO, and under Conventional Personailty, ASTRO tab, set "RX Unmute Rule = Selective Squelch", and under "ASTRO Talkgroup Options" tab, check the Talkgroup box, and select the desired TG from your list.

Make sure the Network ID is entered correctly under Zone/Channel Assignment.

See this thread for more information on finding out the NAC:
http://batboard.batlabs.com/viewtopic.php?f=4&t=80899

You will be able to conventionally scan the voice channels, and the radio will only unmute on the programmed TG. If it's a busy system, expect to miss some transmissions, as the radio has to sample each busy channel for a longer time to decode the TG from the voice frames.

[nmfire10]

I could be wrong but I believe the talkgroups 515 is describing is only for CONVENTIONAL astro, not trunking. They are effectively the same as a multi-PL conventional analog channel. I don't think that has anything at all to do with trunking talkgroups which is what he is trying to do.

[RKG]

I could be wrong but I believe the talkgroups 515 is describing is only for CONVENTIONAL astro, not trunking. They are effectively the same as a multi-PL conventional analog channel. I don't think that has anything at all to do with trunking talkgroups which is what he is trying to do.

That is how I, too, interpreted the OP's question.

[515]

The P25 voice frames have the talkgroup values imbedded in them, whether they're conventional or trunked. You can see them if you tune a P25 service monitor to the trunked voice channels, or just program up the XTS to display the conventional TG on receive. Of course you need to have the correct voice channel NAC in the XTS for that to work.

Actually the trunked voice channels have the TG value in about every other frame, and the TG value occurs in every frame for the conventional channels. The Motorola radios seem to cope with this fine when monitoring the trunked voice channels in conventional mode, but many other brand P25 radios get a little confused when they receive frames without the TG values...

[nmfire10]

I see. Well that's pretty cool. So in theory, you can put in all the channels in the trunk system, put in only the TG you want, put the radio in scan, it will be almost sort of kind of do something resembling trunk tracking.

[515]

Yeah, it works ok as long as the sysem isn't very busy. Since the TG occurs every other frame, the radio has to pause on each busy channel a few hundred milliseconds to check the TG...

It works real well on one UHF trunked system I monitor, as it's set up for "home channel" trunking, where all transmissions occur on one channel, unless it's already busy... I can just park the Astro Saber on it, set to display the TG on receive, and see which TG's are active on the system. No scanner needed! The system isn't usually very busy, so about 95% of the activity occurs on the one channel. And the Astro Saber always stays muted on the encrypted ones that it doesn't have the key for, which most P25 scanners don't do.

[DEMCERT14]

You should be able to pick and choose which TG's you want to listen to with an XTS... You'll have to know the NAC (Network ID) that used on the voice channels, though.

First, under Conventional, ASTRO Systems, Astro Talkgroup list, create your list of TG's. You'll have to enter these TG's in decimal format, as opposed to hex in the trunking section.

Then, program all the voice channels in as ASTRO, and under Conventional Personailty, ASTRO tab, set "RX Unmute Rule = Selective Squelch", and under "ASTRO Talkgroup Options" tab, check the Talkgroup box, and select the desired TG from your list.

Make sure the Network ID is entered correctly under Zone/Channel Assignment.

See this thread for more information on finding out the NAC:
http://batboard.batlabs.com/viewtopic.php?f=4&t=80899

You will be able to conventionally scan the voice channels, and the radio will only unmute on the programmed TG. If it's a busy system, expect to miss some transmissions, as the radio has to sample each busy channel for a longer time to decode the TG from the voice frames.

I got all the talkgroups that I wanted to monitor entered in decimal format into my "Talkgroup List 1". I've also programmed all the frequencies from the trunking system as conventional Astro channels assigned into a Zone by itself. I've set the "RX Unmute Rule" to "Selective Squelch", and the proper talkgroup is selected from the talkgroup list. However the NAC is set as "F7E" since I am still unable to find the proper NAC of the system. So I'm still picking up all radio traffic on the system rather then just the talkgroup(s) I want to hear. Ideas?

[nmfire10]

Yep. Find the NAC.

[DEMCERT14]

Thank you "515" for your help! Your suggestion works. The issue that I am now facing is that I didn't realize that there was an upgrade in the site and they have added on additional frequencies into the trunking site. From the original 8 frequencies, it has been expanded to 23 frequencies. Is there anyway that I can get my XTS2500i to scan this system successfully in conventional mode?

[nmfire10]

Well in that case I think I can say for sure this time that you're screwed. You would think with all this technology, that /\/\ would have come up with more than 16 channels to a scan list. Kenwood radios can scan every channel in the radio if you so desire. M, not so much.

[tvsjr]

Almost like it's, maybe, not a technical limitation but something else... like response to a perceived legal issue?

[nmfire10]

A legal issue making them not want to let you scan more than 16 channels??????

[Pj]

\thread hijack

The last Moto radio that I am aware of that let you scan more than 16 channels was the X9000, circa 1985? It was written in the manuals then, that scanning more than x amount of channels should be avoided so that you do no miss traffic on other channels. To me, thats sort of a slap to the head as if your parked on channel 44 with traffic - if you have 4 or 40 scan list memebers - it doesn't make a difference. In all the configurations of X9000's I had with 64 channels - most, if not all in the scan list - I never had a problem with pri or sec priority scanning.

Maybe for some people/radio's it was an issue. I dunno.

At least on the ASTRO25 series radios they bumped up the talkgroup scan to 15 vs 10 on the ASTRO line.

/thread hijack

If you do not use your radio to xmit, your best bet is to sell it and grab a nice high end scanner. It will be much more flexable and user friendly than ANY motorola radio for trunked systems.

[greyhat]

Im not sure if this is what your looking for but i had a similar issue scanning a trunking network in conventional with both analog and P25 clear/&encrypted digital transmissions on it.

If you set up your personalities to be mixed mode, digital squelch and set encryption to be strapped to "key 16" BUT set to clear and you dont program a key into "key 16" then 99% of the time the digital encrypted transmissions get skipped , digital clear and analog transmissions come through

You can of course set the mixed mode to astro only if you want to hear pure digital clear talkgroups, I have not been able to lock down to individual talkgroups however it does allow P25 "in the clear" talkgroups to come through without affiliating onto the trunked network.

I could of purchased a top of the line scanner but i find it more convenient to have one radio programmed with public safety recieve only, my business channels and citizens band UHF channels (i am in Australia)

With scanning more than one list have you tried creating a personality from "scan list 1" that calls "scan list 2" then at the end of "scan list 2" a personality that calls "Scan list 1"? This should extend your "scanning list"

I hope this information provides some help as it was the best solution i could come up with my myself at the time.