There’s a paradox in amateur radio: after all the time and effort spent getting a license and all the expense of getting some gear together, some new hams suddenly find that they don’t have a lot to talk about when they get in front of the mic. While that can be awkward, it’s not a deal-breaker by any means, especially when this Pi Pico SSTV decoder makes it cheap and easy to get into slow-scan television.
There’s not much to [Jon Dawson]’s SSTV decoder. Audio from a single-sideband receiver goes through a biasing network and into the Pico’s A/D input. The decoder can handle both Martin and Scottie SSTV protocols, with results displayed on a TFT LCD screen. The magic is in the software, of course, and [Jon] provides a good explanation of the algorithms he used, as well as some of the challenges he faced, such as reliably detecting which protocol is being used. He also implemented correction for “slant,” which occurs when the transmitter sample rate drifts relative to the receiver. Fixing that requires measuring the time it took to transmit each line and adjusting the timing of the decoder to match. The results are dramatic, and it clears up one of the main sources of SSTV artifacts.
We think this is a great build, and simple enough that anyone can try it. The best part is that since it’s receive-only, it doesn’t require a license, although [Jon] says he’s working on an encoder and transmitter too. We’re looking forward to that, but in the meantime, you might just be able to use this to capture some space memes.
Thanks to [CJay] for the tip.
Great use case for a 2040 PIco. I’ll never get sick of those microcontrollers or projects like these. Seeing individuals be able to purchase a 3 USD board and some 50 cent components wire up what is otherwise a product is an awesome reminder of the time we are living in.
Very nice.
A faster way to send images over a narrow band radio channel is to use the open-source Assempix. You can run it on a smartphone, no custom hardware needed. The built-in forward error correction is a bonus.
Indeed! Anything to help the sad state of affairs that is SSTV software is welcome! Looking forward to seeing this project progress.
It’s not just the software that’s in a sad state, but SSTV as such.
And not just since now, it had been in that state since the early 90s, at least. :(
The somewhat common QSL card -like pictures (-with pics of big breasted chicks, of course-) speak volumes.
Back in the days of original 8 seconds SSTV, the mode had been used in ordinary QSOs, still and not just on dedicated frequency.
Hams could have an ordinary voice conversation and then embed some quick pictures and drawings.
“Hey, Peter! I have a visitor in my shack! It’s my cat. Wait, I’ll switch the scan converter on!”
Or they could have sent a picture of their own picture. Either via radio or via music cassette/mail.
The music cassette was a cheap/compact medium, albeit unreliable.
Operators without a camera could use a flying-spot scanner to scan a photograpy.
Documentary: https://www.youtube.com/watch?v=kaVMrGkLWk4
Later, there were events like Voyager 2 Saturn Commemorative, which used Frame Sequential Color SSTV for some pictures.
https://www.qsl.net/kd2bd/sstv.html
Frame Sequential mode used three separate 8 second pictures (red/green/blue).
Green was closest to a monochrome picture, so b/w viewers used it.
Pictures could be taken with monochrome camera and a color wheel.
(DigiView frame grabber for Amiga computer worked same way.)
https://www.youtube.com/watch?v=yqHcZzvD9Bs
In early 80s, Robot 36 was more popular than Frame Sequential mode.
The then-current Robot 1200c scan converter had been used, even on STS missions.
https://www.rigpix.com/textandimaging/robot_1200c.htm
https://www.youtube.com/watch?v=41y2ITIS8AE
The classic Robot 400 could have been upgraded/modified to color, too.
https://www.rigpix.com/textandimaging/robot_400.htm
https://www.rigpix.com/textandimaging/robot_400c.htm
Eventally, the MIR orbital complex had used Robot 36, too.
You saw pictures of the crew or pictures from the outside (like a webcam).
It had used a then modern, compact Tasco MR 70 slow scan converter and a PictureTel camera.
Transceiver was a Kenwood TM-V7 (Blue Wonder?).
https://www.rigpix.com/kenwood/tmv7a.htm
https://www.rigpix.com/textandimaging/telereader_tsc70.htm
https://www.dk3wn.info/wp/satelliten/mir/
There had been three SSTV units made for MIR, I think.
One was lost during re-entry.
Later, ISS switched from Robot 36 to PD120, which allowed for pictures in full VGA resolution.
Robot 36 was more complex, though, due to tight timings.
Nowadays, some cube sats still send SSTV pictures, too.
But normal SSTV communication is still rare.
I forgot to mention, the original SSTV has also been used on ships on sea at one point.
The idea was that, for example, doctors on land could view pictures of injured/sick seamen and make a diagnosis.
Info: https://seefunknetz.de/sstv.htm
These were serious, noble applications for SSTV, I think.
What hams nowadays do on 14,230 MHz has nothing to do with real SSTV anymore, I think.
It’s no better than FT-8 or a nasty contest, is it?
Figure out how to do the equivalent of echolink for texting and you’ll have a hit on your hands.
The echolink app for android does do text, I’m not sure how to do it with a radio though.
I played with ham radio SSTV for a while several months ago. I created my own images using a version of Stable Diffusion, and they were all colorful, weird, and unusual. Almost every image I got in return was bland, boring, or just plain stupid. Just stock pictures of women or cars or similar.