SDRTrunk SDR Trunk Audio Question

[bburkett]

To the vast experience/knoledge base here:

I have been running an SDRTrunk setup for several weeks and inspite of a lot of tuning, setting changes and hours of research and forum reading, I can't seem to get consistantly good complete audio.

My computer has a Core i5-6500 3.2Ghz 4 core processor, 16Gb of RAM and 128Mb SSD. I am using 3- genuine RTL-SDR v3 dongles. I have added the option in the start up command file to allocate additional memory (" -X4ms4g"). The dongles are staying on frequency showing 0.1ppm error or less.

I am monitoring 2 control channels. I am within 1/2 mile of one tower (simulcast system) and probably >20-30 miles from the other in another county . For the simucast system, I am within raange of other towers. I seem to get better audio from the more distant system. I have adjusted the gain in many comninations, but can't seem to get the magic one! Perhaps a good explanation of the master, mixer, lna and vga gain settings will help, although I have tried many combinations trying to max the SNR ratio.

I have tried different versions of SDRTrunk, and am currently running the latest nightly release.

I have attached 2 audio file links and screen shots of the 2 RTL-SDRs that are on control channels. Along with cut-off and garbled audio, I also get a lot of audio that is empty other than low "static".

https://drive.google.com/file/d/1i3HKYSZpdVJylAkIW19YgHpOwrwHnlyp/view?usp=drive_link

20231204_080430.481.mp3

drive.google.com

I would appreciate any insight into what I can change or adjust!

Regards,
Bob

 

[bburkett]

Correction to my post: added to the startup command file "Xms4g", not "X4ms4g" !!
~Bob

 

[mtindor]

For the simulcast system you are monitoring with a site 1/2 mi away from you, you should have your gain turned down really low. Any site a half mile away is going to be hitting the frontend of the SDR pretty hard. Make sure you are using Modulation:LSM in the configuration of the simulcast system (at least that's my recommendation).

If the other SDR is monitoring the same band, but an out of county site, it's probably still going to get pumped pretty hard by the RF signals eminating from the local simulcast site 1/2 mi away -- and you may not be able to turn your gain up to where you'd like it to be.

Keep in mind that at times, in the waterfall, everything might look peachy. But when the local simulcast is active and that local site 1/2 mi from you is transmitting on multiple freqs, it may really cause some interference for any/all of the dongles if the gain is not turned down to a reasonable level.

 

[bburkett]

For the simulcast system you are monitoring with a site 1/2 mi away from you, you should have your gain turned down really low. Any site a half mile away is going to be hitting the frontend of the SDR pretty hard. Make sure you are using Modulation:LSM in the configuration of the simulcast system (at least that's my recommendation).

If the other SDR is monitoring the same band, but an out of county site, it's probably still going to get pumped pretty hard by the RF signals eminating from the local simulcast site 1/2 mi away -- and you may not be able to turn your gain up to where you'd like it to be.

Keep in mind that at times, in the waterfall, everything might look peachy. But when the local simulcast is active and that local site 1/2 mi from you is transmitting on multiple freqs, it may really cause some interference for any/all of the dongles if the gain is not turned down to a reasonable level.

mtindor:

I have been thinking it may be gain issue, but haven't been able to pin it down.
I have tried the gain low on the simulcast SDR, but I will experiment more.
The distant system idoes give better audio. I will try cutting back on this system gain, but I do lose it if I cut back too much.

Thanks for you time!

~Bob

 

[dave3825]

Not sure which system is which but the gain on the Summerset is way to high. Noise floor is higher than Cheech and Chong. Go into that tuner tab and take it off automatic, start at a lower value and keep bumping up just until the noise floor starts to rise.

 

[bburkett]

Not sure which system is which but the gain on the Summerset is way to high. Noise floor is higher than Cheech and Chong. Go into that tuner tab and take it off automatic, start at a lower value and keep bumping up just until the noise floor starts to rise.

Thanks, Dave.
I'll give that a try.
~Bob

 

[bhall7]

Could someone provide an overview of what the various gain settings mean? (Master, Mixer, LNA, VGA)

I've always just left it on Auto, but I can definitely appreciate times when one might need to reduce gain, as is the case with @bburkett, with a broadcast site so close to his location. I'd just like to know which one (Master, Mixer, LNA, or VGA) to adjust in this scenario. Thanks!

 

[bburkett]

Could someone provide an overview of what the various gain settings mean? (Master, Mixer, LNA, VGA)

I've always just left it on Auto, but I can definitely appreciate times when one might need to reduce gain, as is the case with @bburkett, with a broadcast site so close to his location. I'd just like to know which one (Master, Mixer, LNA, or VGA) to adjust in this scenario. Thanks!

Bhall

I agree and would appreciate a good explanation of these controls.

I am really impressed and appreciative of all the hard work being put into this project. I really have not been able to find detailed explanations of several areas.

 

[bburkett]

@bhall7 I found this info after some digging. It helps some.

I apologize for not noting the sources!

"As far as the gain stages are concerned – the LNA gain is the first stage and thus the most important – it determines the SNR. Mixer gain is less important (unless the signal is too weak). The VGA gain should be almost always set to zero as it doesn’t contribute to the SNR at all while keeping the dongle warmer and so more thermal noise."

and

"It's the gains of the tuner in rtl-sdr. you have LNA, Mixer, and VGA.
VGA is the last gain, with a quite wide adjustment range.
You can use them to adjust where in the tuner the gain is done, in order to get various optimizations.
VGA gain is used to get the most dynamic range from the ADC, while mixer & LNA is used to deal with the RF and various effects.
LNA works full input bandwidth of the rtl-sdr (sensitive to other strong signals)
Mixer works around the tuned frequency (not very sensitive to stuff far away)
VGA is the gain of the filtered signal, and can be tuned to for best signal performance.
It does take some experimenting to get an idea about how it all behaves.
Too much LNA gain with strong signals, and you see them at the wrong frequency.
Mixer gain, I haven't explored so much.
VGA gain just distort the tuned slice, if you make signals hit the top."

 

[bburkett]

Help! I posting again in hopes of getting new advice. I have tried all recomendations from here and elsewhere.

After gain adjustments, adding a signal attenuator, changing dongle badwidths, making sure Java version is current, changing antennas, making sure tuner ppm's are 0 or close, cutting down to one P25P2 system with a small number of TGs and trying multiple SDRT versions beta, alpha and nightly, I am still getting garbled cutoff audio!

My system has a Core i5-6500 4 core 3.20GHz processor, 16GB RAM and a 128GB SSD and USB3.0 ports. Java memory is 8GB. OS is Ubuntu 22.04 Desktop and has 3 dongles with correct RTL-SDR drivers. I am within 1/2 mile of one of the systems towers which is a new P25 Phase2 simulcast system.

What the heck am I missing??

Any and all help will be greatly appreciated!

Thanks for your patience with my issue!

~Bob

 

[noamlivne]

Help! I posting again in hopes of getting new advice. I have tried all recomendations from here and elsewhere.

After gain adjustments, adding a signal attenuator, changing dongle badwidths, making sure Java version is current, changing antennas, making sure tuner ppm's are 0 or close, cutting down to one P25P2 system with a small number of TGs and trying multiple SDRT versions beta, alpha and nightly, I am still getting garbled cutoff audio!

My system has a Core i5-6500 4 core 3.20GHz processor, 16GB RAM and a 128GB SSD and USB3.0 ports. Java memory is 8GB. OS is Ubuntu 22.04 Desktop and has 3 dongles with correct RTL-SDR drivers. I am within 1/2 mile of one of the systems towers which is a new P25 Phase2 simulcast system.

What the heck am I missing??

Any and all help will be greatly appreciated!

Thanks for your patience with my issue!

~Bob

I don't think I read your previous thread and I don't have experience with Linux, but perhaps a recording of the garbled voice + screenshots of ALL the SDRTrunk windows and tabs can help people here in assisting you.

 

[bburkett]

Here is a screen shot of current configuration operation

 

[dave3825]

A pic of the active control channel on the spectrum as well as the channel tab might show something, like this

 

[MrAmericanada]

Across the top menu click "VIEW"
click "USER PREFERENCE" or push "U"
In the "Audio" section...
select "output/tones"
on the right side drop down select your speakers????

Maybe?

 

[dave3825]

The op is having an issue with sound quality, not audio output selections. And I believe the tones are preemptive tones to play on what’s selected as far as certain types of calls and or data events.

I still believe it’s a signal issue. I run an instance of sdrt on a pc with much lower specs than the op machine and the audio sounds good.

 

[maus92]

Can we ask the OP about the individual SDRs he is using? Make and model of each? Are all adjusted properly? I noticed that one is using a relatively high adjustment for ppm. I don't believe there is a signal issue in terms of received power, or s/n - it's way better than I have here with 2 systems and 3 sites, yet I experience little warbling or audio distortion (just the typical P25 muffling.) I would start by backing down the gains to a point where the signal is unusable, then start adding back gain.

 

[bburkett]

Across the top menu click "VIEW"
click "USER PREFERENCE" or push "U"
In the "Audio" section... View attachment 153060
select "output/tones"
on the right side drop down select your speakers????

Maybe?

I have audio, but it is garbled/broken/cutoff at times. Quite frequently.

 

[bburkett]

Can we ask the OP about the individual SDRs he is using? Make and model of each? Are all adjusted properly? I noticed that one is using a relatively high adjustment for ppm. I don't believe there is a signal issue in terms of received power, or s/n - it's way better than I have here with 2 systems and 3 sites, yet I experience little warbling or audio distortion (just the typical P25 muffling.) I would start by backing down the gains to a point where the signal is unusable, then start adding back gain.

My RTL-SDRs are genuine ones v3. I have tried a very wide range/combinations of gain settings. Comments are much appreciated!

 

[dave3825]

How does it sound if you try it with just one dongle. Some calls will be heard and those out of reach will be missed, but trying that way eliminates a few variables like gain and ppm settings on the other dongles. If you try one dongle and it sounds noticeably better, than it could point to settings not being right on the other dongles or maybe even a usb issue. First rule in troubleshooting is eliminate as many variables as you can. Get to where it’s good and then start adding dongles back.

 

[bburkett]

Thanks for you time to reply! In trouble shooting, I believe that I have found the noise may be causing the issue. I have located the antenna outside and added ferrites on the USB leads. I added 6" USB cables to avoid plugging the dongles directly into the computer. So far I have seen positive improvements! I'll report back.