Linux: gqrx and DRM (digital radio mondiale)

[Andy Stewart]

Hi Linux users,

I am wondering if any of you have listened to the shortwave digital radio mondiale transmissions with gqrx.  I tune them in with gqrx, record the audio in a WAV file, and then play the wave file in the Dream software.  It works, but I was wondering if there was a way in real time to listen to the station.  I see that gqrx can create a UDP audio stream but Dream will not consume it.  I'm looking explicitly for a Linux / Free Software solution. 

Thanks,

Andy
KB1OIQ

[Alexandru Csete]

Hi Andy,

If Dream can use pulseaudio as input device, then you can configure it
to read the output from gqrx. It is built into the pulseaudio system.

THere is description of the setup in these two posts:
http://oz9aec.net/index.php/gnu-radio-blog/463-gqrx-and-pulseaudio
http://www.pe0sat.vgnet.nl/decoding/unix-tlm-decoding/

If dream only uses ALSA then similar triuck can be done using snd-aloop:
http://www.george-smart.co.uk/wiki/Meteor_Scatter_Reception_on_RTL-SDR

I hope this helps you in the right direction.

Alex

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[Andy Stewart]

On Sunday, February 14, 2016 at 12:27:03 PM UTC-5, Alexandru Csete wrote:

THere is description of the setup in these two posts:
http://oz9aec.net/index.php/gnu-radio-blog/463-gqrx-and-pulseaudio
http://www.pe0sat.vgnet.nl/decoding/unix-tlm-decoding/

If dream only uses ALSA then similar triuck can be done using snd-aloop:
http://www.george-smart.co.uk/wiki/Meteor_Scatter_Reception_on_RTL-SDR

I hope this helps you in the right direction.

HI Alex,

Yes, that most definitely pointed me in the right direction.  I have it working!  The pavucontrol settings were the magic that I needed.

I have been able to listen to a digital radio mondiale station, and also to decode CW and RTTY via fldigi.

For everyone's benefit, let me describe what I did to hear a digital radio mondiale station with gqrx and dream on Linux:

a) start the gqrx program, and tune into a digital radio mondiale station (USB and 10KHz filter width)
b) start the dream program
c) start pavucontrol
d) in pavucontrol, click the input devices tab and set the internal microphone levels to zero on both channels
e) in pavucontrol, in the playback tab, be sure that gqrx and dream are both shown.  I set gqrx autio output to be "simultaneous output to build-in audio analog stereo", and the dream receiver output to "built-in audio analog stereo"
f) in pavucontrol, in the recording tab, the dream receiver gets its input from "monitor source of simultaneous output to build-in audio analog stereo"
g) in the dream program, Settings->sound_card->signal_input->device->combined_monitor

I've noticed that I hear both the dream output and the gqrx output in the speakers.  Adjustment of various volume levels reduces the gqrx output to nearly inaudible out the speaker, but plenty of signal for dream to decode.

Thanks, Alex!  This has been most helpful!

Andy
KB1OIQ

[Andy Stewart]

I've attached a screenshot of my DRM reception to this post.

Have a lot of fun, and 73,

Andy
KB1OIQ

[Alexandru Csete]

On Sun, Feb 14, 2016 at 10:18 PM, Andy Stewart <andys...@comcast.net> wrote:
>
> I've noticed that I hear both the dream output and the gqrx output in the
> speakers. Adjustment of various volume levels reduces the gqrx output to
> nearly inaudible out the speaker, but plenty of signal for dream to decode.

Oh, I forgot about that. Although I have not tried it myself,I know it
is possible to create virtual devices in pulseaudio that can be used
for routing. I searched Google for the terms pulseaudio loopback and
found many interesting hits. In particular, this post by G0HWW seems
to contain exactly what we need:
http://www.g0hww.net/2013/11/using-null-sinks-with-pulseaudio.html

Alex

[David Ranch]

Thanks for detailing that all out Andy!  Very cool and I was actually thinking about DRM the other day though more specifically, I wish we could decode HD-Radio on the FM broadcast bands.  Seems that's a proprietary codec and there aren't any SW solutions out there.  Blows me away that companies think this is the way to make money.. this is only INHIBITING me from listening to their stations.  Duh!

Oh well...  back to bookmarking all the different signals I'm hearing in the HAM bands with the SDR!

--David
KI6ZHD

[Andy Stewart]

David:  The details will be in a text file that I'll include with the next version of "Andy's Ham Radio Linux" (probably in a month or two, we'll see).

Alex:  I haven't yet tried the virtual devices.  I got sidetracked by tuning WEFAX stations in GQRX and sending the audio to fldigi for decoding.  :-)

Have a lot of fun and 73,

Andy
KB1OIQ