Trying to use rtl_fm, etc

Alan Corey alancorey at yahoo.com
Mon Dec 31 05:29:24 UTC 2012


With rtl_fm, I get a tiny burst of audio about once a minute.

My dongle is a vendor ID 0x0bda, product ID0x2838 from http://www.amazon.com/gp/browse.html?ie=UTF8&marketplaceID=ATVPDKIKX0DER&me=A2JO7YP9I9Y3D6

I did:
rtl_fm -f 88500000 - | play -t raw -r 24k -e signed-integer -b 16 -c 1 -V1 -

I got:
Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000013

Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle
Found Rafael Micro R820T tuner

-: (raw)

  Encoding: Signed PCM
  Channels: 1 @ 16-bit
Samplerate: 24000Hz
Replaygain: off
  Duration: unknown

In:0.00% 00:00:00.00 [00:00:00.00] Out:0     [      |      ]        Clip:0
Oversampling input by: 42x.
Oversampling output by: 1x.
Buffer size: 8.13ms
Tuned to 88752000 Hz.
Sampling at 1008000 Hz.
Output at 24000 Hz.
Exact sample rate is: 1008000.009613 Hz
Tuner gain set to automatic.
In:0.00% 00:00:00.68 [00:00:00.00] Out:16.4k [ =====|===== ]        Clip:0
^CSignal caught, exiting!


The dongle works if I boot into Windows, but in OpenBSD I can't get anything out of it.  I'm still trying to get dependencies for Gnuradio together.  The only odd thing is that being OpenBSD, there's no -lrt when I link.  Those functions are built into something else so I compile without the -lrt.  There isn't an -lrt library.

I've tried writing little scripts to run it so I do it consistently.  My wide FM one:

#!/bin/sh
rtl_fm -W -l 0 -f 88500000 - | play -t raw -r 32000 -e signed-integer -b 16 -c 1 -V4 -

Narrow:
#!/bin/sh
rtl_fm -N -l 0 -f 162550000 - | play -t raw -r 32k -e signed-integer -b 16 -c 1 -V4 -

I've played with various options.  If I use -R it runs for a long time with lots of data by Sox's meter, but I don't hear anything.  If I pipe it to a file (without -R) the file is very small and grows slowly, not what I would expect from audio.  I just grabbed a fresh copy by git yesterday but it works about the same.

A fresh run:
freebie# rtl_fm -N -f 162550000 - | play -t raw -r 32k -e signed-integer -b 16 -c 1 -V 4 -
Found 1 device(s):
play: SoX v14.3.2
  0:  Realtek, RTL2838UHIDIR, SN: 00000013

Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle
Found Rafael Micro R820T tuner
Oversampling input by: 42x.
Oversampling output by: 1x.
Buffer size: 8.13ms
Tuned to 162802000 Hz.
Sampling at 1008000 Hz.
Output at 24000 Hz.
Exact sample rate is: 1008000.009613 Hz
Tuner gain set to automatic.
Signal caught, exiting!

I don't have much idea what's going on, but I'm tempted to try opening it from a pipe (in C) to see if I can capture anything more.

  Alan

-----
Radio Astronomy - the ultimate DX
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