On the original H4TNC which I uploaded hastily July 10 I found several serious bugs. I have been on the road the past 6 weeks and did some updates and build a simple White Gaussian Noise channel simulator into the H4TNC for testing (I don't have my HF channel simulator with me here in the RV!)
I believe this version is considerably better but I had to make some changes that are NOT compatible (different character coding) than the original 1.0.1 H4TNC version.
Feel free to download the 1.0.2 H4TNC version and play with it. BOTH ends must use this new version. If you can run a full duplex test setup (where the sound card can capture at the same time it is playing) you can use the new test options in the Test drop down menu to send a Quick Brown Fox test mixed with White Noise at -10, -5, 0, 5, and 10 dB S/N (standard 3 KHz Noise Bandwidth). Try squelch values between 3 and 6. Typically 4 or 5 should work best.
When I get back (about 2 weeks) I'll be able to do more extended testing and make some new updates. I also will start work on a ARQ version of the H4 TNC.
Summary of the differences and similarities between H4TNC and V4TNC.
1) Both use same 4FSK modulation at 46.875 baud (200 Hz bandwidth)
2) H4TNC uses lower latency hamming encoding (11,4 code shortened to 8,4 with a minimum Hamming "distance" of 3. V4 uses Viterbi encoding.
3) H4 sends a sync symbol every 1 sec (every 8 characters) to allow rapid resync.
4) Both use soft decoding.
Have fun...good luck. I may try to setup for some test QSOs on the way back. (had some trouble with my tuner earlier).
This is early alpha software...if you need bulletproof and fully verified code ....best to wait a while!!!
Rick Muething, KN6KB
H4FSK TNC Revision History
Date: Rev Change Summary
Aug 21, 2013 0.1.0.2 Modify Two tone command.
Change Character encoding from 8,4,4 extended hamming to expand hamming distance slightly
Modify H4Demod.Decode8BitCharacter to pass EOT (value = 4) to TNC's character crawler
Modify SearchForTwoTone to H4Demod.SearchForTwoTone62B3.
Add mechanism in basic setup to select tuning range (+/- 50Hz to +/- 150 Hz)
Add simple White noise channel simulation to do loopback test on Quick Brown fox at -10, -5, 0, 5, 10 dB S/N
July 10, 2013 0.1.0.1 Initial Alpha release FEC only