SoapyAudio with gqrx

[Charlie Hotel]

Hi
I have been trying to use gqrx with a home made direct conversion IQ receiver usind the laptop sound card.
I have SoapySDR (0.8) installed which provides a sound card IQ input.
Using gnu radio, the generic SoapySDR block works OK with driver=audio in the device chain field and chan=stereo_iq in the stream chain field.
However in gqrx, there is no stream chain field and adding chan=stereo_iq in the device chain field has no effect: the sound card input is converties to mono and gqrx shows a symétrie Spectrum, symptomatic of real only data input.
Any clue on box to tell soapy to use IQ data in gqrx?
Ubuntu 22.04
Gnuradio 3.10 (from ubuntu repo)
SoapySDR: libsoapysdr0.8 from Ubuntu repo
Gqrx: gqrx-sdr from Ubuntu repo
73 de F1EVY
Bernard

[Dave Baxter]

Hi.

Check that the audio input you are using, is actually a STEREO input.

Most laptop built in inputs are for mic, or headset+mic, so though stereo out, are usually mono input.

An external soundcard will also be less noisy, as well a true stereo input.

Hope something helps.

73

Dave G8KBV 

If it aint broke, hit it harder.

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[Charlie Hotel]

Hi Dave,

Yes I am using line input. It is actually a stereo input. I can use it ok with gnuradio or Quisk. With gnuradio, i can either use the audio source or the Soapy source with success (ie IQ samples and full non symétrie Spectrum). To get there using Soapy source i need to use the chan=stereo_iq let in the stream chain field of the Soapy source block.

However there is no such field in the io device configuration box of gqrx… 

My problem is I have not found a way to tell the Soapy-audio-device driver to output stereo. It seems to add I and Q together and serve GQRX a mono left stream…

73

Bernard 

Le 28 déc. 2025 à 19:32, 'Dave Baxter' via Gqrx SDR <gq...@googlegroups.com> a écrit :



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[Mike Sutherland]

Helo Bernard, did you download the 2 GQRX programs from the Ubuntu
Software bin, the 2nd one is GQRX tools
that may help
Cheers Mike

> To view this discussion visit https://groups.google.com/d/msgid/gqrx/E6BFA3A1-4FCB-48EC-A1B1-87F0CE4BF96E%40free.fr.

[Charlie Hotel]

Thanks Mike
I’ll try that and see if it helps!
Cheers
Bernard

> Le 28 déc. 2025 à 21:52, Mike Sutherland <ve3...@gmail.com> a écrit :
>
> Helo Bernard, did you download the 2 GQRX programs from the Ubuntu

> To view this discussion visit https://groups.google.com/d/msgid/gqrx/CAOnNCBv2cwaiYJsO6%2BC22%2B1NqN5HRWPxS1VvneZopQPoi4eSPA%40mail.gmail.com.

[Charlie Hotel]

Hi Mike
Not sure I have gqrx_info on the repo.
Did you mean soapysdr-tools which provides SoapySDRutil —info command?
Cheers
Bernard

> Le 28 déc. 2025 à 21:52, Mike Sutherland <ve3...@gmail.com> a écrit :
>

> Helo Bernard, did you download the 2 GQRX programs from the Ubuntu

> To view this discussion visit https://groups.google.com/d/msgid/gqrx/CAOnNCBv2cwaiYJsO6%2BC22%2B1NqN5HRWPxS1VvneZopQPoi4eSPA%40mail.gmail.com.

[Charlie Hotel]

Hi Mike,
I confirm there is no gqrx-tools Pocket on the Ubuntu repo.
$apt-cache search gqrx only returns gqrx-sdr and multimon-ng
I have soapysdr-tools installed though.
Cheers
Bernard

> Le 29 déc. 2025 à 08:08, 'Charlie Hotel' via Gqrx SDR <gq...@googlegroups.com> a écrit :
>
> Hi Mike

> To view this discussion visit https://groups.google.com/d/msgid/gqrx/8E9E73A7-FF6A-4CD2-9F60-3A5C013198CB%40free.fr.

[Dave Baxter]

Morning Bernard.

OK, understood, I too have one laptop (an old WinVista era machine, repurposed.)  That does also have a true "Stereo Line" input, but it is still very noisy compared with even an ancient external SoundBlaster 16 on USB.

I used to mess about with SoftRock RX's in the past (on Windows) with dedicated simple RX tools that could extract a signal, and that's all.   That would have been used for automated HF beacon monitoring, but then our electricity costs went through the roof, so 24/7 operation of PC's became expensive!

The external SB16 was at least 10dB quieter (so more sensitive) than the built in sound device.    That machine is an old Toshiba Equium, with an AMD single core CPU, and ATI Rage graphics.   That was a fast/slick machine in it's day.   The huge screen and full size keyboard are still nice, but modern OS's with only 4G of available RAM (the maximum it can handle) run sluggishly these days, even Puppy Linux!.

The only thing I've done with SoapySdr, was to rebuild it and link in the "binary API blob" from SDRPlay, to get their V1 RX working on LMDE 5.   As before, one then has to recompile GQRX with the new SoapySDR tool, to get everything working, and that was a chore I found then, even when the older QT5 dependencies could be found.  I don't know enough to port the whole lot to the current QT environment.   I'm using LMDE 6 these days (for now) in effect Linux Mint, without the Ubuntu stuff.

I found though, that it all had a creeping "lagg" in the recovered audio compared to the visual spectrum display.  A memory leak somewhere perhaps, if left running long enough, a couple of days, it would crash and burn.

GQRX is a nice application when it works, but sadly seems to be approaching the status of Abandonware, much like GPredict too.   (Unless anyone knows different.)

Unlike many, I "don't get on well" with C/C++.  Odd really, as that is the only programming language I've ever had formal training on!   Since then, I spent way too many years at the past day job, working with Pascal code under Delphi on Windows, 3.11, 95, 98, 2000, XP, 7, and a bit on Win10.   Quite a long time...

(Lazarus using FreePascal on Linux is very close to how Delphi was in the past.)

I hope you get your SDR setup working in the end.  The feeling when you've done something like that from scratch almost, is wonderful indeed.

73.

    Dave.

[Bruce]

See some of my earlier postings on lag with Gqrx. There are two distinct forms of lag I've seen, depending on the number of clock masters in a setup!

Yes, there can be audio lag, as you have seen. There can also be lag between the signal and the spectrum display too, in the case of RSP SDRs.

Cheers,
Bruce

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[Charlie Hotel]

Dave, Bruce, Mike

Thanks for your advice.

I finally found a workaround to use gqrx with sound card input. Not very convenient but it works:

-create a named pipe to providence a file input to gqrx: $ mkfifo /tmp/gqrx_fifo 

- create a simple gnuradio flow-chart with:

  - An Audio source bloc, mapped to the Line input where my sdr base and is plugged

  - a float to complex bloc to convert the stereo_iq to gnuradio complex

  - a file sink bloc, mapped to the fifo

Launch gqrx and sélect the file IQ input device, with the sapine rate as in the audio source bloc in grc (48000 in my case)

Launch the gnuradio flowchart

Ta—dahhhh, magic works !

73 de F1EVY

Bernard 

Le 29 déc. 2025 à 12:03, Bruce <abruce...@gmail.com> a écrit :



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[Dave Baxter]

Well done.

The fact that you got it working is the important event.   Nicely done.

73.

Dave

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[Charlie Hotel]

Thanks Dave!

Gnuradio’s really the Swiss knife!

Bernard 

Le 30 déc. 2025 à 17:11, 'Dave Baxter' via Gqrx SDR <gq...@googlegroups.com> a écrit :



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