Woo hoo! Please tell me about anything you'd like me to present at
Hamvention. This will definitely be in there.
On Thu, Apr 19, 2018 at 6:51 PM, David Rowe <da...@rowetel.com> wrote:
> Hello,
>
> I've been working steadily on FreeDV 700D, porting from Octave to C, and
> working through some tricky sync problems. I can now simulate the end-end
> system on the command line, and listen to the results. It's outperforming
> FreeDV 1600 by about 10dB on fast fading channels, and is error free at
> -2dB SNR on AWGN channels.
>
> The main differences from FreeDV 700C are a new OFDM modem with rate 1/2
> LDPC code and the option of a long interleaver (seconds of latency). It
> uses the the 700 bit/s codec, although with a few tweaks we could run other
> codecs and LDPC codes using a few dB more SNR. More inf on the FreeDV 700D
> mode here:
>
> https://www.rowetel.com/?p=5573
>
> For anyone who would like to play along, here's README_ofdm.txt for the
> mode:
>
> https://svn.code.sf.net/p/freetel/code/codec2-dev/README_ofdm.txt
>
> This includes references to blog posts, lots of command line examples, and
> specification at the end. There's enough information for the super keen to
> run it over the air using the cmd line tools, which I haven't done yet.
>
> Next steps are some over the air tests, write a freedv_api.c "mode" for
> it, integration into the FreeDV GUI program, and lots of tweaking.
>
> - David
>
> On 16/04/18 08:52, Glen English wrote:
>
>> I will write more abt this when I return, however a) the quality of the
>> capacitor influences notch depth, b ) getting the area and proximity of the
>> loop to the line matters. for a 6" filter, anything over 33db for 600k
>> bp-reject is very good.
>>
>>
>>
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--
Bruce Perens K6BP - Standards committee chair, license review committee
member, Open Source Initiative
President, Open Research Institute
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