A quiet month for me, as I spent much of August hiking the Larapinta trail, a rugged 230 km walk in the middle of Australia.
However I did have some time for a little FreeDV work. I spent some time finalising an upcoming QST article on RADE, working with the good people at the ARRL.
Most of the time was spent tracking down a subtle issue thrown up by verification procedure – the “loss” metric of the C version of RADE V2 was found to be sensitive to the timing offset (thanks Mooneer for finding this one). Turns out this was an AGC algorithm error, which I have been working on correcting, testing, and documenting. I’ve had this experience before – e.g. when manually porting between Octave and C for previous FreeDV modes.
These days with agentic coding the port is (e.g from Python to C) quite fast (~ 1 day compared to months doing it manually) – but for these subtle bugs a human guiding the AI was definitely required to track down the root cause. Claude, however, deserves the credit for suggesting we try running without AGC which finally trapped the issue.
Hello,While FreeDV works great on HF, there is a big challenge when using it over the geostationary satellite QO-100. Due to standard LNB temperature drift, the frequency shifts constantly, causing the FreeDV modem to lose sync frequently.Would it be possible to implement a simple, software-based AFC / EFC (Automatic Frequency Control) feature inside FreeDV, similar to Fldigi?A basic AFC that can automatically track and lock onto the center frequency as it drifts by a few Hz would completely solve the LNB drift issue on QO-100, making FreeDV ideal for satellite communications.Thank you for your amazing work on this project!
Babis sv1uh
RADEV2 is supposed to be able to adjust frequency by a few Hz but I don’t know if it’ll be sufficient for QO-100. Worth a shot, anyway!
-Mooneer K6AQ
Hi Babis – we have specifically excluded tracking the large and rapidly changing frequency offsets required satellite operation in the requirements for RADE V2.
– David
Thank you both for your fast and clear answers!I understand your technical choice for RADE V2 and the focus on HF operations. Since software-based AFC inside FreeDV is out of scope for now,
I am always at your disposal to help with testing. We are looking forward to the release of Version 2!Thanks again for your incredible work on the FreeDV project.
Babis sv1uh
A view years ago, when we tested FreeDV 2020 over the satellite, David changed the decoder to a differential mode, and it worked.