Sunday, June 4, 2017

SSTV: It's Getting There

Rainy weekend, so it's time to play with radio hardware – and curse at linux software, all relating to slow-scan TV (SSTV).  At least the software is free.  Note that this is not "TV-TV" as in moving pictures and all that, but more akin to faxing color still photos over high frequency radio waves very long distances.  Sending moving pictures (boy, does that phrase sound old-timey) takes a lot of bandwidth, about 5MHz.  Sending these low-res stills takes less, about 3KHz.  That's more than a thousand times less, and about the same as voice communications.  Again, pretty similar to faxing over a telephone voice line.  Just without the telephone or line.

Here's a typical, moderately strong SSTV signal on 20 meters.  The call sign indicates that it was sent from Michigan.

hard-linked to Linux laptop ($150+headache), SignaLink ($100+mostly harmless), QSSTV software (free+headache)... 

over-speaker audio linked to iPhone ($50 special+easy), Black Cat CQSSTV app ($3+easy):

Hmm.  These two images are off of the same signal, same radio, acquired at the same time.  The first one is definitely better, but the second one was definitely easier.  Not sure I'd want to conduct a conversation while editing text on the iPhone on the fly, but it is at least a viable backup.

On the whole, both are pretty good and each has its advantages.  Still a few more things to do before I'm ready to hit transmit however.

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