SSTV

Slow scan television!

SSTV is a method for transmitting images that was pioneered by ham radio operators. It transmits images using a very narrow bandwidth, approximately the same as a single sideband (SSB) voice signal - 3 kHz. It is essentially a translation of image data into audio tones that can be transmitted over the radio, and then back into images.

Why is this a big deal? First, because normal, moving television images require signals with a bandwidth 2,000 times larger (6 MHz). This saves a huge amount of spectrum space, making this mode usable on lower frequencies (HF/VHF) and not just restricted to higher frequencies. SSTV is also cheaper - you aren't operating microwave transmitters and drawing thousands of watts to transmit your signal. You can use existing equipment and radio transceivers designed for SSB voice signals at a bandwidth of 3 kHz. This makes it easy to receive an SSTV signal with a VHF radio and pipe it over to a sound card for slow scan TV software to take over.

The technology dates back to 1968, when amateurs were first granted spectrum space to do slow scan TV. Slow scan TV was also utilized during the Apollo lunar missions.

You can find a sample of what slow scan TV signals sound like here: File:JupiterSSTV.wav

Software

Qsstv