These days, sending a picture to someone else is as simple as pulling out your smartphone and sending it by email or text message. It’s so simple a child can do it, but that simple user experience masks a huge amount of complexity, from the compression algorithms in the phones to the huge amount of distributed infrastructure needed to connect them together. As wonderful and enabling as all that infrastructure can be, sometimes it’s just too much for the job.
That seems to have been the case for [Dzl TheEvilGenius], who just wanted to send a low-resolution image from a remote location. It turns out that hams solved that problem about 70 years ago with slow-scan television, or SSTV. While most of the world was settling down in front of “I Love Lucy” on the regular tube, amateur radio operators were figuring out how to use their equipment to send pictures around the world. But where hams of yore had to throw a considerable amount of gear at the problem, [Dzl] just used an ESP-32 with a camera and some custom code to process the image. The output from one of the MCU’s GPIO pins is a PWM audio signal which can be fed directly into the microphone input of a cheap portable transceiver.
To decode the signal, [Dzl] used one of the many SSTV programs available. There’s no mention of the receiver, although it could be pretty much anything from another Baofeng to an SDR dongle. The code is available in the article, as is an audio file of an encoded image, if you just want to play around with the receiving and decoding side of the equation.
We could see something like this working for a remote security camera, or even for scouting hunting spots. If you want to replicate this, remember that you’ll need a license if you want to transmit on the ham bands — relax, it’s easy.
I did something simar with a DRA818 module. (The PCB part is still unfinished.)
https://github.com/Antiemes/SSTV/tree/master/code/esp-idf
It was 1957 or 58 that Copthorne Mcdonald had a series in QST. So 65 years. Late sixties it started to take off.
I’m tired of the stories of how hard it used to be. People built be ause that was the way to get results. If they hadn’t experimented, there’d be no SSTV today.
A monitor wasn’t so hard, and in the late sixties there was an article in QST about converting an oscilloscope. You had to build a whole camera, thiugh flying spot scanners allowed fixed images to be sent with a bit of electronics added to the monitor. One of the first leaps in the seventies was sampling converters for CCTV cameras, easier to come by and you could make adjustments fast by viewing on a tv set.
“I’m tired of the stories of how hard it used to be.”
I’m tired of certain things , too, but that doesn’t belong here.
Personally, I do have a small collection of all those vintage things you mentioned.
From what I can tell, things are not as trivial as they seem.
Adjusting things is tricky. Remember! This was in the 60s, when grid-dip meters were state of the art and oscilloscope a highly sought after item.
As for the other problems, we’ve forgotten nowadays: The storage medium. There’s flutter, if you’re using low quality tapes/cassette systems. For example.
Then there’s the problem of sync signals.
They somewhat improve stability (slant) if received properly. But if lost, say due to lots of QRM on shortwave, a whole line is lost.
That’s why modern SSTV and later Robot-8 compatibles systems do use “free running” mode and do ommit the sync signals. The result are skewed/slanted pictures. That issue was far less apparent in the 60s.
That’s one of the reasons why old 7s/8s monochrome equipment has issues with modern SSTV software. The software lacks the sync signal. Also, there’s a different in aspect ratio. An old Robot/Wraase converter uses 1:1 aspect ratio, modern software uses 4:3.
The list goes on..
Robot-36 as used my MIR/early SSTV was far from simple – it’s the most complex SSTV, afaik. Just to name an example.
Vy73s, Joshua
Very cool. I had something similar going with a pi zero… you can transmit fm on one of the gpio pins. Not very powerful but simple. A little imagemagic and camera!! Maybe esp32 has frequency enough to output fm on a gpio to skip the transmitter?
If you do things like this, please study up on your radio theory, get licensed, and for everyone around you, apply proper filtering.
YSK that this is a really ‘rude’ way to transmit FM. The harmonics crap all over the spectrum.
Can the same not be said for using a baofeng? lol…
The power output from a non amplified 3.3v gpio pin is pretty limited. Might be fun to try a fox hunt with…
It makes a baofeng look pretty tame: https://hackaday.com/2018/04/03/filter-your-pi-and-be-a-responsible-pirate/
It’s certainly a lot less powerful than the sort of unlicensed transmitters you can pick up on aliexpress (ironically, given the prices right now, for a lot less than a rPi) but I’d stick to something a bit less horrible.
I was waiting for someone to filter one of the Baofeng’s. Of course Andreas Spiess provided one of the more elaborate approaches I’ve seen:
https://www.youtube.com/watch?v=CIeT4SWneeo
I applaud the effort put into this, I myself have contemplated building something similar, but time and a lack of coding skills have prevented me from getting it done.
One solution for those not ready to build something from parts is to use an Android phone with a headphone jack and whatever sstv app you prefer. I’ve done it before and beyond adjusting your output volume to something closer to line out levels. I’ve done it with a bunch of radios and it works really well.
PUT THIS ON A WEATHER BALLOON!
note you can monitor SSTV world wire at websites like
World SSTV Cam’shttps://www.worldsstv.com
many of the web SDR support a SSTV receive mode look for kiwi-SDR sites…
the best SSTV mode for use over a web based SDR seems to be modes NR-73, NE-115 etc…
hold up better with random timeing of SDR over the web.
http://72.253.112.147:8073/