Three or four years ago, Jeremy allowed me to 'push the boat out' a bit (as regards NBTV) by showing 405-line television, encapsulated in a complete System A signal on VHF Channel B1, passed across the convention room on a modulated light beam.
I haven't had time this year to do any NBTV as such, since all my efforts have been devoted to building the new London 405-line transmitter (currently we are facing the challenge of how to make an efficient vision-sound combiner, working at power output level).
Anyway, this year I needed to rustle up something quick to bring to the convention along that could be made ready in a few days. I've pushed the boat out a bit further. So this time I shall be popping a System B signal in colour on Channel E4 onto a light beam and sending it across the hall. The resulting picture and sound will be viewable on my 1982 JVC 5-inch colour set.
These days, modulating light beams at prodigious rates with digital signals is routine for fibre internet and the like. What is unusual about my efforts is that this is high speed linear modulation of an LED at VHF, preserving all the gradations and characteristics of the analogue AM and FM carrier signals. Maybe someone better informed than me can comment on the stringency of the linearity requirement for digital...
Steve O