now that I’ve got a little more free time on my hands,
I’ve decided to look int the issues with the APT decoder again.
So back in January I open a merge request with a gnuardio port of my code from GitHub - LongHairedHacker/apt-decoder: Automatic picture transmission encoder in Rust
The code syncs to A and B markers in the signal continuously,
instead of just once, which pretty much corrects all of the slanting.
Initially it seemed to work perfectly.
However at some point it stopped working without any changes done to my code, producing even worse images than before.
I’m trying to reproduce the issue by replicating the decoder does using the audio files for this observations.
apttest.grc.txt (20.2 KB)
This flowgraphs takes the 49kHz audio from observations, re-samples it to 62.5kHz like in the original flow graph, does the exact same filtering and feeds it into the NOAA APT sink from the gr-satnogs master.
Now we’ve got a new problem: The resulting png looks perfectly alright.
So there must be some difference between the audio from the file and what is being used in the regular decoder flowgraph.
So hints on what I might be missing here would be highly appreciated.
Currently the only thing that I can think of is that audio written to the file been down-sampled to 48kHz and hence has a smaller bandwidth.
This may filter out some artefacts, that otherwise cause trouble for my line syncing code.
Other than that I’m currently out of ideas.
Also thanks to Alexander for spotting my typo and opening a merge request:
Unfortunately this is not cause of the problem.