Re: [Discuss-gnuradio] new to GNUradio: AFSK and codec2 gmsk modem

[Kristoff Bonne]

Hallo Marcus,



On 29-07-13 01:44, Marcus D. Leech wrote:
> > - My first step with GNUradio was to learn a bit more about using it;
> > so .. do some test.
> > I wanted to use GNUradio to determine the width of an AFSK signal; so
> > I started looking for a AFSK modulator / demodulator; to come to the
> > conclussion I didn't find one.
> > I looked in the GR source, on CGRAN, using several generic search
> > engines without look.
> > Am I missing something here? I would be surprised there is no AFSK
> > modulator / demodulator in GR as it would mean one cannot do
> > packetradio or APRS with gnuradio.
(...)


> Just found this, it might help:
> https://github.com/dl1ksv/gr-afsk
Hmmm. Looks interesting. A good start. :-)


However, it seams I have another problem: it does not build on my system 
(ubuntu 12.04 LTS).
It needs gnuradio-runtime and as I currently run gnuradio 3.6.4.1 + 
Boost 1.49 build from source, it doesn't have that.

I tried to build 3.7.1 -which seams to include gnuradio-runtime in its 
source- but that fails on a number of tests (qa_fir_filter, 
qa_freq_xlating_fir_filter, qa_constellation_receiver and 
qa_codec2_vocoder).

Grrr! :-(


> Also, keep in mind that AFSK is a kind of "double modulation scheme".
> To demodulate it, first demodulate the FM-voice using a narrowband
>   FM demodulator, then run that into a suitaby-configured FSK demod.
> AFSK was always a "hack" to allow you to send data over narrowband
> FM-voice radios without having to do anything to the radio.  So, they
> chose
>   Bell-202 synchronous modem tones, because they'd "fit" in most
> narrowband FM-voice radios.
Well, that is exactly the reason I would like to test it out. :-)

We currently do packet/ax.25/aprs at 1200 baud AFSK, which is not that 
much less then the 1400 bps needed for codec2. Add a little bit frame 
sync-patterns and -perhaps- some FEC, we might end up with 1600.


It would be kind-of-nice to be able to try out DV with standard FM 
handhelds without any need to have a radio that does 9k6.
But, this is for me just as much a practicle test and just a way to 
getting to know GNUradio. :-)



Cheerio!
Kr. Bonne - ON1ARF