Recording video in the 1950s

[Mike Watterson]

Maybe a toy - but to have achieved video recording onto a compact cassette is an astonishing feat nevertheless!

By not actually recording "real" video! It was clever and if they could have got the price down would have been more successful.

Only nearly nine times normal cassette playback speed at about 16.875 ips, only a bit more than twice 1950s BBC audio tape. So how?
They recorded on FM carrier a bespoke analogue video of only 120 × 90 pixels @ 15 fps, i.e. 90 line TV. Using the ASIC to read the CCD and feed a DAC.
On Playback (and preview) the ASIC used an ADC and converted that to regular monochrome NTSC @ 30 fps with a large black border using a frame store.

So the cleverness was the ASIC design, not the tape transport or head which was mainly a primitive video conversion from a format like later mechanical TV to regular monochrome NTSC. About 120 lines seems to have been the peak of purely mechanical TV as the 240 line Baird system scanned a "near real time" photographic film using a flying spot CRT and a CRT display. In the Netherlands even earlier lower resolution mechanical TV scanning had used CRTs for display. Cold Cathode CRT was 1987 simultaneously in England and Germany. Zworykin developed sealed, high-vacuum cathode ray tube with a thermionic emitter in 1931 which led to Oscillograph/Oscilloscopes. But there were earlier poorer CRTs from 1920. Yes, the same Zworykin that later solved the electronic camera issues (Farnsworth's was a dead-end as it only had instantaneous charge as beam hit spot, Zworykin's accumulated charge for entire frame duration!)

It wouldn't be hard to emulate a better Pixelvision now using a cheap phone camera, Raspberry Pi and and FPGA, maybe even a reprogrammed existing standards converter and record on cassette tape. Power consumption would be rather higher! The Pixelvision only used one cassette track for video.