I thoroughly enjoyed working on the Digivision project and it inspired me to try SSTV for myself. Commercial equipment like the Robot 1200C was way out of my league price-wise, so the homebrew approach was the only option. I briefly had a crude system running on the BBC micro. I think the program used screen MODE 2 with the 8 colours it offered providing 8 shades of grey when viewed on a monochrome monitor. I seem to recall using a dither routine to produce extra shades. I somehow tortured the Beeb’s built-in sound system into producing the required tones for transmit. This would have been around 1985/86 so the SSTV mode would of course have been 8 second black-and-white.
Realising that the BBC micro’s graphics were not good enough for colour SSTV, I started working on ways to supplement the Beeb with external hardware. Although I had little knowledge of digital electronics at the time, I had learned how Static RAM chips worked whilst experimenting with “sideways RAM” on the Beeb. It occurred to me that by using binary counters to address the devices I could generate a standard video signal to drive an RGB monitor. With a lot of help from my good friend Jack Edgecock, G1NZH, I designed a system based around 16K x 8 static RAM chips with a display resolution of 256 pixels by 256 lines and 16 levels of red, green and blue. Although officially christened the “ColourStore 2000” the device was always simply known as “the Framestore”. It had no on-board processing; all that was carried out by a BBC micro connected via the Beeb’s 1MHz bus.
I seem to remember building and selling around 6 of these devices. The high price of RAM at the time made it an expensive project, and although much cheaper than systems like the Robot 1200C, it never really took off. Regular users at the time included G4IJE, G3JMA, G0PKH, G7KCS, G1EVD and G4PAD.
Mike, G3JMA, and I had a stand at the BATC (British Amateur Television Club) show at Harlaxton Manor around 1990/1 where we displayed the Framestore system. I recall that we went two years in a row, and although there was a lot of interest we didn’t actually sell any!
The photo above shows a prototype Framestore as built by me and then somewhat modified by G3JMA. The top board is a video digitiser comprising three CA3306 6-bit analogue-to-digital converters. In those days, long before digital stills camera and the internet, a video camera connected to a digitiser was the main method for generating your own pictures. As far as I know, the Framestore in the photo still works, although I have unfortunately lost all the Beeb software that would be required to make it do anything useful.
The Framestore software included the Martin and Scottie modes (as implemented on the Robot 1200C scan converter) and I used it to make the first ever colour SSTV contact between the UK and USA on 6 metres (50MHz) in 1989. See photo below from QST magazine, February 1990.