PL/CTCSS/DCS squelch on rtl_fm?

James Sharp james at
Mon Dec 9 18:17:17 UTC 2013

On 12/9/2013 7:33 AM, Chris Hanson wrote:
> Thanks for the response.  I looked at the code and from what I can tell,
> it’s just using various ham radio rigs built in CTCSS facilities and
> programming them via RS232.  Am I missing something?

The app_rpt file has some functions to detect tones in an audio stream 
that can be used to detect the CTCSS tones.  Look through the 
"tone_detect" function along with the goertzel_* functions.

They're not specifically tagged as functions to decode CTCSS tones, but 
they should be able to be used as such.

Those functions are expecting to be fed a 16-bit signed linear mono 
audio stream.

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