SDRTrunk Military P25 Phase I Trunking 380mhz 25khz Channels Not Working with SDRTrunk

[brian86]

I am trying to monitor a 380mhz P25 Radio System and SDRTrunk (Latest Version) will not lock on to the control channel. I am pretty sure I see why, but can't figure out how to correct the issue.

Military P25 Seems to be 25khz Wide Band Frequencies and it seems the SDRTrunk Program can't lock on to the wide band control channels. This may not be the case but I don't have any other clue to why its not working. Is there a way to adjust the bandwidth per system/channel in SDRTrunk? Attached are some screenshots of SDRTrunk when trying to lock on to the control channels. Also this system is only about 2 miles from me and all other traditional scanners are monitoring this system just fine with a full signal strength.

Any help would be appreciated.

P.S. There are 2 additional tuners available. So it is not a lack of tuners causing this issue.

Thanks, Brian

 

[GTR8000]

P25 control channels are no wider than 12.5 kHz regardless of the band or application (public safety, military, etc.)

I would suggest posting a better screenshot that actually shows the 380 spectrum in the top/waterfall display, rather than showing us your 700 MHz spectrum.

 

[GTR8000]

Since you likely have all 10 frequencies for NAS Patuxent River programmed, I would increase the control channel rotation delay to at least 750ms, maybe even 1000ms to make sure SDRTrunk has enough time to lock onto the active control channel. If that doesn't do it, figure out what the currently active control channel frequency is, and temporarily remove all other frequencies from the channel definition and see if you get a lock on the control channel. Oh yeah and make sure you have the modulation set to C4FM for that system, as it's not simulcast.

 

[thewraith2008]

Is it possible that this is TETRA and not P25.
TETRA is 25 kHz.

Simple test would be to try SDR# with the TETRA Demodulator plug-in to see if it can decode it as TETRA.

 

[GTR8000]

Is it possible that this is TETRA and not P25.
TETRA is 25 kHz.

Simple test would be to try SDR# with the TETRA Demodulator plug-in to see if it can decode it as TETRA.

Yeah no, it's absolutely not TETRA, it's a 380 MHz P25 U.S. military system that has been around for ages.

 

[thewraith2008]

OK, I only mention it because you said:

P25 control channels are no wider than 12.5 kHz regardless of the band or application (public safety, military, etc.)

 

[campd715]

I am trying to monitor a 380mhz P25 Radio System and SDRTrunk (Latest Version) will not lock on to the control channel. I am pretty sure I see why, but can't figure out how to correct the issue.

Military P25 Seems to be 25khz Wide Band Frequencies and it seems the SDRTrunk Program can't lock on to the wide band control channels. This may not be the case but I don't have any other clue to why its not working. Is there a way to adjust the bandwidth per system/channel in SDRTrunk? Attached are some screenshots of SDRTrunk when trying to lock on to the control channels. Also this system is only about 2 miles from me and all other traditional scanners are monitoring this system just fine with a full signal strength.

Any help would be appreciated.

P.S. There are 2 additional tuners available. So it is not a lack of tuners causing this issue.

Thanks, Brian

View attachment 174159View attachment 174160

Why does the subject line say "...not working with DSDPlus" when the issue being discussed is SDRTrunk?

Dennis

 

[DSheirer]

I am trying to monitor a 380mhz P25 Radio System and SDRTrunk (Latest Version) will not lock on to the control channel. I am pretty sure I see why, but can't figure out how to correct the issue.

Military P25 Seems to be 25khz Wide Band Frequencies and it seems the SDRTrunk Program can't lock on to the wide band control channels. This may not be the case but I don't have any other clue to why its not working. Is there a way to adjust the bandwidth per system/channel in SDRTrunk? Attached are some screenshots of SDRTrunk when trying to lock on to the control channels. Also this system is only about 2 miles from me and all other traditional scanners are monitoring this system just fine with a full signal strength.

Any help would be appreciated.

P.S. There are 2 additional tuners available. So it is not a lack of tuners causing this issue.

Thanks, Brian

View attachment 174159View attachment 174160

In your screenshot of your 380-MHz channel, you might be confusing the noise floor for a signal. When using the polyphase channelizer in sdrtrunk, all channels are filtered to 25 kHz with 2x oversampling and that produces a noise floor that rapidly rolls off at either end of the spectrum and visually this can cause it to appear like a 25 kHz wide digital signal versus the (actual) empty channel that you're seeing in your screen shot. That's one of the nice benefits of polyphase channelizer is this adjacent channel rejection.

Alternately, if the channel frequency doesn't (exactly) align with one of polyphase channels, sdrtrunk will compose a new channel by recombining 2 adjacent channels, mixing to recenter the desired signal, and then down sampling by 2 ... in that case, you'll see a more traditional noise floor that doesn't rapidly roll off at the channel edges.

To compare, select one of the Phase 1 control channels that is actively decoding above and see how the signal appears relative to the noise floor in the Channel view.

BTW ... your thread title may be a bit misleading?

Denny

 

[RaleighGuy]

380 MHz systems (not encrypted) work great on a Unication G5 pager, and there is one available in that band (rare find) in the RR classifieds now. Full disclosure, it's mine but system I was using it on changed systems and went encrypted, I have 2 G5 pagers so letting this one go.

Unication G5-B with 700-800MHz and 380-430MHz & Standard Charging Base

Like new G5-B pager for 700-800MHz and 380-430MHz, with standard drop in charger (no box, uses AC adapter and cable for pager), screen protector that has been on since purchase, has newest firmware (2.02), includes one new charging/paging cable...

forums.radioreference.com

 

[M105]

I am just using FMP24 with DSDPlus to monitor a local 380 MHz P25-1 military system and it works fine for me. I can't speak for SDRTrunk but my experience would make a case that DSDPlus isn't the problem.

Try setting up FMP24 / DSDPlus (Fastlane) in a single dongle trunking arrangement and see if that works.

 

[enosjones]

sometimes 380 defaults to AM, make sure the modulation is fm and see if that works

 

[GTR8000]

sometimes 380 defaults to AM, make sure the modulation is fm and see if that works

He's using SDRTrunk, not DSD+ (thread title/tag is incorrect). SDRTrunk does not sometimes default to AM, so this is not the issue.

We'll have to wait for the OP to return to address the pointers I mentioned in my two posts.

 

[maus92]

@GTR8000 is correct in advising to lengthen the channel rotation dwell time to 750ms or longer. The PAX River 380 P25 system uses L3Harris infrastructure, and they are notorious for requiring a more lengthy delay. We have two L3Harris systems in my area and they absolutely need it to prevent SDRT from stepping through the control channels.

 

[brian86]

I am sorry, I was very tiered when I posted this. I have since been able to get the system to work after pulling my remaining hair out. I followed the steps provided and set the longer dwell time and it fixed the issue I was having. Also it is SDRTrunk and Not DSD+.

I thank all of you for your responses. It has been very helpful.

***Forum Admin Please Change my "DSDPlus" tag to "SDRTrunk" if possible***