Beginner question - what to do with RAW files?

[Sam Imberman]

Hi,

I'm just getting started with SDR, and right now I am trying to record some audio from the local weather radio. I've read and watched lots of tutorials and forum posts, and in everything I've seen, gqrx outputs directly to .wav files. For me, however, gqrx is outputting .raw files. I'm wondering if someone can help me understand what exactly is happening, since I'm getting nowhere in my research.

I understand from other posts that the .raw files are IQ data, which I understand to be raw received radio information. Apparently it is possible to pass these files through sox and generate .wav files. I found one post which encouraged me to run .raw files through sox like so:

sox -r 48k -t raw -e s -b 16 -c 1 -V1 ./gqrx_20171216_194848_162550000_80000_fc.raw foo.wav

... but this only produces garbage. Unfortunately, I only understand about half of the command options. But if I understood the exact parameters of the .raw file, maybe I could figure out the right sox settings on my own.

Another thought I had was that apparently gqrx uses gnuradio for its audio output, so it might be possible to directly pass the .raw files through gnuradio. However, it looks like gnuradio is usually taking .wav files in. So I still appear to be missing a link to take me between .raw and .wav.

In summary, I am trying to figure out how to get from the output .raw files to a .wav file that I can do things with, and I would appreciate any push in the right direction!
Thanks!

Sam

[Alexander Fasching]

The IQ recorder outputs *.raw files, which contain the whole received
spectrum, not just the frequency you've selected. This is independent of
the selected demodulator. It depends only on the sample rate and the
center frequency. It's everything you see on the waterfall.

If you want to save demodulated audio, you have to use the audio record
option in the audio dock. This one produces *.wav files at 48k sample rate.

If you haven't already read it, you might want to check out this guide:
http://gqrx.dk/doc/practical-tricks-and-tips
The section "Audio frame" contains information on recording audio files
which can be played in any audio player. The sample rate is 48000 and it
contains only the spectrum selected by the bandpass around the offset
frequency.

In an analog radio, the IQ file would be the band selected by your
bandpass (e.g. 14.000MHz to 14.250MHz), while the audio file contains
only demodulated audio at a certain frequency (the one you have tuned
your radio at).

Regards,
Alexander Fasching, OE5TKM

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[Sam Imberman]

Thanks a lot! I understand now that I was using the wrong "recording" functionality.

All my best, and I hope I have more advanced questions soon.

Sam

On Sat, Dec 16, 2017 at 3:55 PM, Alexander Fasching <faschi...@gmail.com> wrote:

The IQ recorder outputs *.raw files, which contain the whole received spectrum, not just the frequency you've selected. This is independent of the selected demodulator. It depends only on the sample rate and the center frequency. It's everything you see on the waterfall.

If you want to save demodulated audio, you have to use the audio record option in the audio dock. This one produces *.wav files at 48k sample rate.

If you haven't already read it, you might want to check out this guide:
http://gqrx.dk/doc/practical-tricks-and-tips
The section "Audio frame" contains information on recording audio files which can be played in any audio player. The sample rate is 48000 and it contains only the spectrum selected by the bandpass around the offset frequency.

In an analog radio, the IQ file would be the band selected by your bandpass (e.g. 14.000MHz to 14.250MHz), while the audio file contains only demodulated audio at a certain frequency (the one you have tuned your radio at).

Regards,
Alexander Fasching, OE5TKM


On 12/16/2017 09:33 PM, Sam Imberman wrote:

Hi,

I'm just getting started with SDR, and right now I am trying to record some audio from the local weather radio. I've read and watched lots of tutorials and forum posts, and in everything I've seen, gqrx outputs directly to .wav files. For me, however, gqrx is outputting .raw files. I'm wondering if someone can help me understand what exactly is happening, since I'm getting nowhere in my research.

I understand from other posts that the .raw files are IQ data, which I understand to be raw received radio information. Apparently it is possible to pass these files through sox and generate .wav files. I found one post which encouraged me to run .raw files through sox like so:

sox -r 48k -t raw -e s -b 16 -c 1 -V1 ./gqrx_20171216_194848_162550000_80000_fc.raw foo.wav

... but this only produces garbage. Unfortunately, I only understand about half of the command options. But if I understood the exact parameters of the .raw file, maybe I could figure out the right sox settings on my own.

Another thought I had was that apparently gqrx uses gnuradio for its audio output, so it might be possible to directly pass the .raw files through gnuradio. However, it looks like gnuradio is usually taking .wav files in. So I still appear to be missing a link to take me between .raw and .wav.

In summary, I am trying to figure out how to get from the output .raw files to a .wav file that I can do things with, and I would appreciate any push in the right direction!
Thanks!

Sam

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