Silence in WAV

[Akito01]

Hello,

I'm using this command on a raspberry with an airspy mini:
./rx_fm -E wav -d driver=airspy -f 137.9125M -g LNA=14 - | /usr/bin/sox -t wav -e signed-integer -b 16 -c 1 - rx_test.wav

but this outputs a wav-file with silence.

Why is this? I'm expecting to hear static noise.

[starvald]

rx_sdr and rx_fm were a quick hack from rtl_fm, it's never worked properly, rx_sdr has been fixed up a bit but rx_fm is complete junk.