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Old 24th Apr 2018, 5:34 pm   #12
1100 man
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Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Frame gated AGC modifications

Having settled on a black level clamp circuit for my Pilot TV, the difference in black level stability is quite remarkable.
However, doing that has shown the limitations of the mean level AGC system fitted to this set. On a bright scene the amplitude of the video waveform changes at the clamp diode and alters the black level slightly.
I could live with it but there is a possible solution I wish to explore. Fernseh has introduced me to the concept of 'frame gated AGC'. This has the potential to give a stable video amplitude irrespective of scene content.
So hopefully a workable circuit can be constructed to achieve this.

All the best
Nick
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