I'm being unable to finish the 1st lesson of http://greatscottgadgets.com/sdr/1/ successfully. The example runs, but instead of being able to capture the tuned radio station, I only get noise. GNU Radio companion keeps printing audio underrun erros.
I'm using GNURadio on a Kali VM on a Mac OS X i7 with 16Gb
On
This may be caused by Pulse Audio, see the wiki.
Please try modifying the ~/.gnuradio/config.conf to:
[audio_alsa]
nperiods = 32
period_time = 0.010
verbose = false
Open the file in a text editor:
nano ~/.gnuradio/config.conf
identify the [audio_alsa] section.
Check the values match the text above.
This should resolve the bitty audio, but the complete lack of radio could mean your signal isn't strong enough or you're on the wrong frequency. Try moving the SDR aerial around, preferably near a window to get a better signal.
For finding radio stations, it might help to replace Scott's channel_freq variable with a slider from GUI Widgets > QT > QT GUI Range. This gives you a slider that will control the frequency, some suggested values but I don't know the full FM range:
Id: channel_freq
Label: Channel Frequency
Type: "float"
Default Value: 100e6
Start: 70e6
Stop: 120e6
Step: 1e3
Wisget "Counter + Slider"
Minimum Length: 200
For anyone else following Scott's guide in 2021, some of the features he's using have been deprecated, such as the WX GUIs, there are replacements for these under QT instead, in particular the "WX GUI FFT Sink" can be replaced with the "QT GUI Sink".
Underrun means that your audio device is not getting the samples per seconds it needs. Maybe it doesn't support the sampling rate you configured it to, maybe your VM is just running too slowly (audio emulation in VMs is especially problematic).
You should try using GNU Radio natively. GNU Radio has a live image that you can put a DVD or USB stick and try out natively.
Also, try different audio sampling rates in the audio sink (you will need to adjust the audio rate/decimation in the demodulator, too!). 44100 works best, typically.