Discussion:
[Freetel-codec2] pairphone modem
Steve
2017-03-25 11:07:55 UTC
Permalink
I was playing around with the pairphone audio. I didn't listen to the
vocoder or even try to see if it worked. The modem was the interesting
part, and an interesting design. Looks like it might be perfect for FM :-)

https://github.com/gegel/pairphone

I believe it is 1200 MELPe, and designed for the analog side of cell
phones. Thus, doesn't require 3G/4G etc.

Here's the spectrum:


​
and the time domain:


​
Here's a link to a WAV recording from my soundcard at 44.1k and resampled
to 8k (so I could see the spectrum closer in).

https://www.dropbox.com/sh/3fjc9srmg1mgrqe/AABt430-vkwNqzokVMzffAA6a

Disregarding all the cipher stuff, it looks kind of fun. A little too wide
for the digital input/output of narrow-band ham rigs.

73/Steve

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