01-11-2018, 10:46 AM
A thought occurs to me, well two really, about that sync cancelled AGC system. It relies on the peak of the inverted video signal being black level and there being no blacker than black signal apart from the sync pulses.
However, on colour transmissions, the subcarrier can be blacker than black under some conditions - mainly saturated red and blue - so would one of these sets adjust the gain from scene to scene when they occurred or was there an HF roll off before the AGC sampling to stop this happening.
I saw very few Murphy sets, so the chances of watching one under the right conditions - time of day, transmission content - was extremely unlikely and also, because 405-line NTSC was only ever transmitted from Crystal Palace, you wouldn't have been in a position to know, Trevor.
It while I was pondering this that the second thought came to me - what happened when the vertical sync broad pulses arrived? Or was there a long time constant involved that smoothed out these imperfection - both chroma and field sync - so that neither could cause any visible effect?
However, on colour transmissions, the subcarrier can be blacker than black under some conditions - mainly saturated red and blue - so would one of these sets adjust the gain from scene to scene when they occurred or was there an HF roll off before the AGC sampling to stop this happening.
I saw very few Murphy sets, so the chances of watching one under the right conditions - time of day, transmission content - was extremely unlikely and also, because 405-line NTSC was only ever transmitted from Crystal Palace, you wouldn't have been in a position to know, Trevor.
It while I was pondering this that the second thought came to me - what happened when the vertical sync broad pulses arrived? Or was there a long time constant involved that smoothed out these imperfection - both chroma and field sync - so that neither could cause any visible effect?
