Hi Brady, David,
I have started transitioning my GRC flowgraphs to C++ and I have put the
code up on Github, just in case you might find it useful in your tests for
the 2400B mode. My choice of a modem is AFSK, 2000 bit/sec (1200 bit voice
or 1300 bit data). It has no FEC, no scrambling and no interleaving (yet).
The audio is framed for the standard 40 msec Codec2. It works through a
handheld FM transceiver and can be decoded easily with Gqrx.
The perfomance is 5 dB worse than analog FM, measured for 12 dB SNR. I
would be very curious to see a comparison with 2400B. My next step is to
transition the DBPSK modem which is 3 dB worse than analog FM based on my
USRP captured data.
Link to the code repo: https://github.com/kantooon/gnuradio_audio_modems
Video of operation: https://www.youtube.com/watch?v=2FZBQvVm5Co
Cheers,
Adrian (YO8RZZ)
On Thu, Mar 17, 2016 at 12:04 AM, Brady O'Brien <brady.obrien...@gmail.com>
wrote:
> Hey Adrian,
>
> The gnuradio-companion pipelines I used for the test are attached. These
> grc pipelines are only meant to get 16-bit 48k samples in and out of the
> HackRF and rtlsdr for testing. The meat of the FSK is done with the C fsk
> modem, used in freedv_rx, freedv_tx, fsk_mod, and fsk_demod. We are also
> running our FSK modem directly from SDR samples instead of through FM
> radios. We will be running 2400B over legacy FM radios, but don't yet have
> the same degree of test coverage.
>
> Thanks,
>
> Brady O'Brien
>
> On Wed, Mar 16, 2016 at 3:34 PM, Adrian Musceac <kanto...@gmail.com>
> wrote:
>
>> Hi David,
>>
>> Is it possible to get our hands on the Gnuradio code? I've been trying
>> to optimize modems running at 1200 bits/second and the best I could do
>> was 100% copy at 8 dB above analog FM for DBPSK and 12 dB above for
>> GMSK. Your modem seems to be 16-20 dB better than that! If I could see
>> the Gnuradio graph maybe I could figure out what I'm doing wrong.
>>
>> Thanks,
>> Adrian
>>
>> On 3/16/16, Steve <coupaydevi...@gmail.com> wrote:
>> > Ha, I wish it was through a radio!
>> >
>> > I'm trying to think what I have laying around here that might make a
>> good
>> > transmitter for it.
>> >
>> > On Wed, Mar 16, 2016 at 4:02 AM, glen english <g...@cortexrf.com.au>
>> wrote:
>> >
>> >> ah. good stuff. nice progress.
>> >>
>> >>
>> >> On 16/03/2016 7:50 PM, Steve wrote:
>> >>
>> >> Just using the script:
>> >>
>> >> freedv_tx 2400A ve9qrp_10s.raw modem.raw
>> >>
>> >> Which produces a RAW audio file sampled at 48 kHz and importing that
>> into
>> >> audacity.
>> >>
>> >> On Wed, Mar 16, 2016 at 3:46 AM, glen english <g...@cortexrf.com.au>
>> >> wrote:
>> >>
>> >>> Hi Steve
>> >>>
>> >>> Nice
>> >>>
>> >>> is that through a PA- if so, linear or linear in say 3dB compression?
>> >>>
>> >>>
>> >>> On 16/03/2016 7:42 PM, Steve wrote:
>> >>>
>> >>> Thought I'd upload a spectrum snapshot. You can't really see the
>> >>> carriers
>> >>> until you drop the number of samples to about 256, but this shows how
>> >>> wide
>> >>> it is.
>> >>>
>> >>> I noticed that the freedv_tx was outputting +/- 1.0 signals and a
>> couple
>> >>> of clips going on. Maybe need to knock it down to +/- .5 like the old
>> >>> FDM
>> >>> modes.
>> >>>
>> >>> FYI
>> >>>
>> >>> Steve
>> >>>
>> >>>
>> >>>
>> >>>
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>> >>>
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