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
<mailto: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 <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
<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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