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[dsp] Bell 202 AX-25 in DSP

Alejandro Santos listas at alejolp.com
Thu Nov 17 19:27:51 UTC 2011

On Thu, Nov 17, 2011 at 1:58 PM, Scott Miller <scott at opentrac.org> wrote:
> I've done pretty simple decoders on 8-bit hardware, with proof-of-concept
> code in Visual C++ if you're interested.
> I've only used the Goertzel algorithm for DTMF decoding.  I don't think it's
> fast enough for Bell 202.

Actually, Goertzel is faster than using FFT if your target is just one
single frequency. My idea is to use Goertzel algorithm to detect just
one of the two Bell 202 tones on an 8 times oversampled stream, 9600

Applying Goertzel on 8 conscutuve samples should give the amplitude of
the frequency. Then, moving the segment 1 sample and repeating the
process should give the rate of change of the presence of the tone on
that segment.

However, my DSP skills are near-zero and I'm looking for comments and/or help.


Alejandro Santos

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