rtl_fm problem with capture audio

Pete Zaitcev zaitcev at kotori.zaitcev.us
Thu Nov 29 17:12:35 UTC 2012


On Tue, 20 Nov 2012 11:59:19 +0200
Vitaliy Kulchevych <coolchevy at gmail.com> wrote:

> $ rtl_fm -f 100.0e6 -N -s 170e3 -o 4 -A -r 32e3 -l 0 - | play -t raw
> -r 32k -e signed-integer -b 16 -c 1 -V1 -

I found that Dave had the right idea about jacking up the sample rate.

But another thing is that rtl_fm just won't work until the signal is
strong enough. With my dongle I saw a decent FM out of the box on
the waterfall display, but rtl_fm just would not grab: outputted
noise and small fragments of corrupt sound that resembled the
transmissions.

Then, I replaced the stock antenna and its long cable with a basic
monopole designed for 1GHz -- way outside of FM radio band! But
immediately rtl_fm started working. Apparently the cable attenuation
was too bad.

Final command line was this:
rtl_fm -l 0 -f 99.5e6 -N -s 170e3 -o 4 -A -r 24e3 - | \
aplay -r 24k -f S16_LE -t raw -c 1

-- Pete




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