Working SSTV via satellite

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Joined: Mon May 01, 2017 5:00 pm

Working SSTV via satellite

Post by hfsdpk11 » Sat Aug 03, 2019 6:24 pm

I've been using an RSP2Pro/SDRUno 1.31 together with MMSSTV with rather good results on the "Remembering W5LFL" event currently running on the ISS but have run into a few issues where I'm looking for some help or guidance.

1. It's been very useful to run the SDRU recorder during a pass so as to replay a pass in case something goes nuts in real time, however I'm finding that during playback, disc access will sometimes momentarily hang SDRU operation which results in the audio being muted for a short time - enough for the SSTV decoder to lose sync and mess the image. This happens randomly and I can see whenever there's a significant disc i/o (the HDD led is on solid), SDRU will do a suspend and resume. I can play back the segment of interest several times and out of that, get only one instance without a disc i/o hanging the audio. Frustrating. I have found that using an external USB3 powered HDD helps quite a bit but it's not perfect, maybe an external SSD would be even better. At any rate, is there any way to buffer the disc i/o so as to fix the SDRU hangup issue? If not, is this something that's even possible in SDRU and could be added to the roadmap for a future release ? BTW, there is no problem with recording; only with playback.

2. My VRX FM-AFC loop has a bias in it which causes the VFO to drift upward in frequency at a rate that's larger than what might be expected from noise alone after the loop loses lock. This is problematic with satellite links that are prone to deep QSB and an unattended, unlocked AFC has a fair chance of drifting out of range before the signal reappears. Ideally, the VFO ought to hold frequency when the AFC loop opens. Is there a config file for SDRU with a parameter to trim the AFC zero bias, as there is no VFO hold in the current SDRU implementation? Failing that, I'd suggest a future enhancement that would add an AFC loop lock indicator on the VRX-EXW window and that when the loop goes below threshold the VFO is locked, to be released and again driven by the AFC error when above threshold. The threshold and lol/acq hystersis could be in a popup window when right clicking on the AFC button.

3. The recorder scheduler is very useful. May I suggest a future enhancement to expand the scheduler as a list of multiple start/stop events rather than be limited to just one. This would allow recording an entire pass group without having to keep the recorder running and gobbling up many GB of noise.

Cheers to all, havin' a ball with my RSP2.

Last edited by hfsdpk11 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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