[amsat-bb] Digtial-SSTV via AO-40

[AA2AE <aa2ae@xxxxxxxxxxxxx>]

All

I've been fooling around with Digital-SSTV on HF for some time and wondered
how the signal would handle doppler shift on AO-40. Digital-SSTV requires a
stable frequency and it seems that without doppler correction, it's
difficult to copy a picture. For satellite work, Digitrx could use an AFC.

I did manage to copy a few pictures this week by changing the picture
transmit time and redundancy settings. Waiting until AO-40 was near apogee
was a big help as well. The shorter transmit time kept the doppler to a
minimum and the high redundancy seemed to help with the errors.

The Digitrx software doesn't have full-duplex capability, so I recorded my
downlink and then played it back through the sound card by looping the
audio. Using the higher redundancy and shorter transmit times causes a lot
of picture compression so the images aren't the best, but it's a start.

I wonder if it's possible to have an AFC built into the Digtial SSTV
software to track doppler?

Has anyone else tried Digital Slow Scan via AO-40?

73, Tony AA2AE


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