SDRTrunk Garbled/Patchy Audio

[Alex Ihrig]

Hello all, I am new to using SDRs and SDRTrunk and have been trying to fine tune my setup. I am attempting to monitor 1 P25 Phase II system (Collier County P25). I am running 3 Airspy R2s at 2.5 mHz all plugged into USD 3.0 ports on my Windows 11 computer. I can provide system specs if needed. I occasionally and randomly am experiencing garbled and choppy audio on talkgroups I am monitoring. Transmissions either cut off completely or the decoding degrades and other talkgroups infiltrate the one I am monitoring, etc. I’ve tried running anywhere from 3-8 MAX channels, no change. I don’t have any errors in Command Prompt and I’m getting any sync loss messages etc. I’ve adjusted my gain settings, no change. The offsets look good. I have very good signal from the tower where I am located and all three R2s have Remtronix 800 mHz antennas attached. I live in an apartment building so any external antenna setup is not an option. My SDS100s have always worked just fine inside with the Remtronix and these work great too most of the time as well. The issue is just persistent enough where I need to do something about it. Please let me know what further information I can provide to better help diagnose my issue. Thanks!

If you’d like to listen to the feed for the garbled audio you can likely find some transmissions with the issue present below:

https://www.broadcastify.com/calls/node/2374

[dave38...@gmail.com]

Post screenshots (3) of your tuners tab showing settings and spectrum for each Airspy. 

[Alex Ihrig]

[Alex Ihrig]

Example audio

On Thursday, April 20, 2023 at 10:22:45 PM UTC-4 dave38...@gmail.com wrote:

[Alex Ihrig]

Additional audio

On Thursday, April 20, 2023 at 10:22:45 PM UTC-4 dave38...@gmail.com wrote:

[Alex Ihrig]

I only had 1 Airspy R2 at first and was using 10 mHz but was still having my audio issues, so I got 3 to fully cover my system at 2.5 mHz each and I'm still having the same issues.

Attached a photo for what it looks like when I use 1 R2 at 10 mHz.

On Thursday, April 20, 2023 at 10:22:45 PM UTC-4 dave38...@gmail.com wrote:

[Noam Livne]

Are the signals you are trying to monitor the two that appear in the first pic with the "Collier Dispatch"?

If so, I would guess that they are too weak for SDRTrunk to work with.

I would compare the reception and decoding with SDRSharp/DSDPlus Fastlane where the reception and sensitivity are better.

I opened an Issue at https://github.com/DSheirer/sdrtrunk/issues/1526

This is something my friends and I are suffering from for a long time now.

When the signal is not strong enough (in the Talk Channels) the audio can be momentarily garbled or totally garbage (even though there is no real signal there and SDRTrunk should have stopped monitoring it, accordingly). (I think that an issue about the garbled audio is already open).

Besides trying to improve the reception somehow (moving the antenna a bit, tweaking the Gain a bit), or using DSDPlus Fastlane, I have no good tips.

[charley....@gmail.com]

There are some signal issues depicted in the first two frames.  The third frame shows too much gain.  Why 3 R2s?  Why limit them to 2.5 MHz?  Three Airspys are going to use a lot of hardware resources.  My office is inside a building where I cannot mount an external antenna, but I am located well within the coverage footprints of the systems that I monitor.  I have used a cheap stick-on window antenna in the past and it worked well.

[charley....@gmail.com]

One Airspy is plenty.  The gain is set too high for this signal.

[Alex Ihrig]

Thank you for the info. I will mess around with those and see what I can figure out.

On Friday, April 21, 2023 at 3:05:09 AM UTC-4 noam...@gmail.com wrote:

[Alex Ihrig]

I will back down the gain and try to keep running 1 R2. I was experiencing issues with garbled audio at 10 mHz and read in multiple posts about how the R2 although rated for 10 mHz did not always perform that well at 10 mHz, so I figured I'd try 3 at 2.5 mHz. Not change unfortunately. So the issue something else. This computer is dedicated for running SDRTrunk so I didn't mind the resource usage if it meant improved transmission.

Specs:

Windows 10 Pro

Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz

RAM 8 GB

[Alex Ihrig]

Messed around with the gain controls and switched 1 to 10 mHz. So far so good it seems.

[Eric F.]

Getting gain just right can take some time. In the spectrum window if your signals touch the top you have gain too high leading to clipping and distortion. More gain equals more signal but that includes noise and interference.  We need just the right signal to reliably decode what we want.
If the system's frequencies are near enough that the bandwidth of the tuner can cover them all then you need only 1 tuner for said system. You can actually get a little more depending on frequencies in use. SDRTrunk will shift around as best it can to stay locked on the control channel and hear all that it can, potentially approaching twice the tuner bandwidth if only the *correct* frequencies are in use at any given time. Naturally that scenario doesn't occur all the time. Rarely is a system more than 10MHz wide. But the basic dongle at 2.8 won't cover it all for many systems.

[dave38...@gmail.com]

Generally I raise the gain high as it can go, to where the noise floor just starts to rise. Then I back it down slightly. 

[Alex Ihrig]

I will continue to play with it. So far the balance I have right now is the best its been so far. Will continue to monitor. Thank you all for your input.

On Friday, April 21, 2023 at 9:33:46 PM UTC-4 ericfer...@gmail.com wrote: