[amsat-bb] Help Needed: GNU Radio + FoxTelem

Zach Leffke zleffke at vt.edu
Thu Oct 8 17:20:38 UTC 2015

Hello Everyone,
     I am frantically rushing to get GNU Radio to 'play nice' with 
foxtelem.  I'm running all linux here.  I'm hoping someone can maybe 
throw me a few pointers on getting the fox telem software to work with 
external SDR applications.  I'm attempting to pipe signals from GNU 
Radio in three ways, all met with failure:

First is by running an FM receiver flowgraph and then trying to pipe the 
audio out via a Linux FIFO using the 'Wav File Sink' block in GR.  I 
point the SDR flowgraph to my pipe, and then I point the FoxTelem 
software to the same pipe and fire the programs up.  I've successfully 
used this method in the past to feed a sound streaming application that 
"thinks" is reading from a standard wav file, but is actually the GR 
flowgraph audio output.  GNU Radio seems to run for a second or two 
(probably the amount of time it takes to fill the buffer) then the Fox 
Telem Software crashes with exceptions:

'javax.sound.sampled.UnsupportedAudioFileException:  could not get the 
audio input stream from input file.'

In gnu radio I'm using the wav file sink with a single port and sample 
rate of 48k and 16bits.  This "appears" to match what FoxTelem is 
expecting, but I'm getting the crashes.

An alternative method I'm attempting is to use a standard audio sink in 
gnuradio (I can hear the audio on my laptop speakers) and then try to 
pipe that into the fox sw with a virtual audio cable.  I'm attempting to 
use JACK and qjackctl, but I have little experience with this and so far 
have failed to get it to do anything other than listen to the soundcard 
mic and line in ports.  If someone knows of a simple to use Virtual 
Audio Cable for Linux so that I can pipe the audio via the sound card 
that would be great and I can give that a go.

The third method I'm trying to get working is by placing the fox sw in 
IQ mode and again attempting to use a 'wave file source' in foxtelem 
pointed at a FIFO to pipe the IQ data from GNU radio into foxtelem.  
again I get the exception mentioned above.  This would be the preferred 
method in my case over the audio piping.  If someone has any experience 
with this that would be great.  For those familiar with GNU Radio I'm 
taking the complex stream (250ksps), reesampling to 192ksps, converting 
to float, then taking the real and complex streams and feeding them into 
a 'Wav file sink' with TWO ports pointed at the fifo, again with 16 bit 
depth and set to 192ksps.  Foxtelem is looking for a wav file at 
192ksps.  I'm hoping the two port file sink allows I data on the right 
channel (in0) and Q data on the left channel (in1).

Any and all pointers would be welcome.

Zach, KJ4QLP

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