sdr trunking question

benskigomez · Dec 23, 2014

Just need a little clarification, I'm using an sdr dongle and unitrunker to monitor a local trunked system. Sometimes I feel as though i'm only getting half of the conversation. There are four different control frequencies listed. Would i need to monitor all four? And if so, im assuming that i would need a dongle for each. Is this correct? Thanks for any help.

SCPD · Dec 23, 2014

You only need to monitor the active control channel. If you are missing calls, this could be caused by a poor decode rate. If some of the calls are encrypted, you won't hear them.

benskigomez · Dec 23, 2014

Thanks for the quick reply, I'm pretty new to sdr's and trunking, but I'm really enjoying them. At least I know I'm on the right track, but why would they have more than one control channel listed? Are they for redundant systems? The system I'm monitoring is zip code 45342 Montgomery County OH.

N7CTF · Dec 29, 2014

Losing control

There is one control channel and one stand by control chan for each radio sysem.. then 2 or more voice channels. One dongle(sdr radio) should monitor the control chan and via software control the other sdr to switch to the assigned voice chan with it's assigned by control.

This site trunking police scannerTylerwatt12.com | Tylerwatt12.com and it's associated video is how I configed my system. It was a "job". ie. watching the vid in HiRez then doing each task but I got it done. :^) There is a LOT to this install but it works.

There's lots of YouTube vids that show just how these trunking systems work.

SCPD · Dec 30, 2014

That setup is much more complicated than is actually needed. Configuring the RTL sticks directly in Unitrunker is simpler, easier, and uses way less CPU.

You want the ability to run SDR# on both RTL sticks - for calibration and doing other non-trunking stuff.

The tutorial on RTL-SDR.com describes release 29.

RTL-SDR Tutorial: Following Trunked Radio with Unitrunker - rtl-sdr.com

Release 30 works even better. The auto correction feature adjusts the warp value to compensate for thermal drift; something SDR# does not do for you.

reconrider8 · Dec 30, 2014

so in 30 theres no ppm adjustment?

fredva · Dec 30, 2014

Unitrunker said:
You only need to monitor the active control channel. If you are missing calls, this could be caused by a poor decode rate. If some of the calls are encrypted, you won't hear them.

I'm experimenting with SDR and Unitrunker. If a system switches to the alternate control channel, is there a way for Unitrunker to automatically determine that and monitor the alternate CC? Or must an individual discover the switch and manually change the frequency to continue monitoring?

n9mxq · Dec 30, 2014

I'm running 30 here with a P25 system. I set the Signal receiver to the known control channel and when I click the channels tab in the Site window it already shows the alternate control channels. I'd be led to believe it would select the proper control channel if the main one went south for some reason.

There is a PPM selection, I set it to what I found for each stick with SDR# and check the DRIFT CORRECT box and Unitrunker takes it from there.. It's a damn handy feature.

altonj · Dec 31, 2014

fredva said:
I'm experimenting with SDR and Unitrunker. If a system switches to the alternate control channel, is there a way for Unitrunker to automatically determine that and monitor the alternate CC? Or must an individual discover the switch and manually change the frequency to continue monitoring?

I think what you are looking for is the 'Chase' feature which (I think) should be on the signal receiver - don't have it available in front of me to check for sure.

fredva · Jan 1, 2015

Thanks for the reply. That sounds encouraging.

reconrider8 · Jan 22, 2015

i click the auto correction and im still getting bouncing signals am i missing something?

SCPD · Jan 22, 2015

i click the auto correction

Make sure you have a good correction value AND you've got a good squelch value (full quieting when there is no signal) before turning this on.

i'm still getting bouncing signals

I don't know what this means.

reconrider8 · Jan 23, 2015

Instead of like a solid green or yellow it will bounce from a solid green to 2 red bars then jump back up

MBaker · Feb 1, 2015

fredva said:
I'm experimenting with SDR and Unitrunker. If a system switches to the alternate control channel, is there a way for Unitrunker to automatically determine that and monitor the alternate CC? Or must an individual discover the switch and manually change the frequency to continue monitoring?

I have that problem as well, the system I monitor changes control frequencies ever 24 hours. I have to then search for the correct one and change it. It would be nice if it would follow the correct control channel.

SCPD · Feb 1, 2015

MBaker said:
the system I monitor changes control frequencies ever 24 hours. I have to then search for the correct one and change it. It would be nice if it would follow the correct control channel.

If a separate SDR program is controlling your SDR receiver, you have to manually tune the SDR to the new control channel.

If your SDR receiver is an RTL stick with an R820T tuner inside, you can configure it directly in Unitrunker as a signal receiver and use the Chase feature described above to recover whenever the control channel has moved.

More info here ...

Chase | Dwell | Discover | Pick Site | Pollution

sdr trunking question

benskigomez

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