SSTV – ROBOT36
Analogue television has existed since the 1930s, and many countries around the world still broadcast some form of analogue video signal. The traditional analogue TV broadcasted approximately 30 video frames per second to produce a steady video image across the television screen. A signal this robust requires a large amount of “bandwidth” or space on the electromagnetic spectrum, each “channel” is a 6mhz slice of this spectrum that was specifically allocated for the broadcast of this signal.
Amateur Radio operators used similar techniques but have far less spectrum available to them. Analogue video processes were therefore developed to use far less than 6mhz of spectrum. Since most HAM radios use analogue audio circuits, the technique required this new low-bandwidth signal to fit the limited bandwidth and requirements of audio transmission and reception. The trade off is where we get the name SSTV or “Slow Scan Television.” By reducing the video signal from six megahertz to a mere three kilohertz a video framerate drops from 30 frames a second to 1 frame in 36 seconds. (though earlier and simpler techniques can provide a simple black and white lower resolution image in as few as 8 seconds) This is obviously a huge drop in quality however it allows international (and even space station to earth) broadcasts of images where terrestrial analogue television signals would breakdown after a few kilometers.
So where does the tapezine fit in?
Because SSTV techniques use audio frequencies, this allows you to use any technology that deals in audio to transmit SSTV images. Because you can convert any image into an SSTV signal, a tapezine can be made by recording that audio signal directly to any audio cassette. SSTV is so robust you can record from your computer speaker to the microphone of a tape recorder, though direct feed from computer to cassette input is best.
How do I decode my tapezine’s images?
Since SSTV techniques are still in heavy use by radio amateurs, software packages that allow encoding and decoding of this data can be found for any platform: Windows, MacOS, Linux, even Android and iPhone. Most of these software packages are free to install and simple to use. Tapezine: The Analogue Journal uses a specific encoding/decoding technique called “ROBOT 36” it is a colour process that takes 36 seconds of audio to transmit each image. Robot 36 software can easily be found online.
Of course, you don’t need to use SSTV specifically with cassettes, you can do it from phone to phone over a speaer, you can email yourself SSTV .wav files or upload them to Youtube. If you have the equipment you can even receive SSTV images from the International Space Station. SSTV images is an analogue format, however digital encoding/decoding software has turned it into a hybrid format. The analogue nature of transmission over audio allows the introduction of analogue “noise” which is a soft distortion of the image as it travels from medium to medium. The noise produced is often aesthetically pleasing, though it can admittedly be a distraction to those accustomed to flawless digital image transfer. SSTV images are also low resolution, and their use on an audio cassette guarantees at least some level of noise and signal loss. You may find it charming, and if you do – I encourage you to play with SSTV.