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Originally Posted by David_Robinson
If the modulator is like my design, the sound modulator is set to System I, negative vision mod, and the input is biased by a preset pot which acts as an adjustment for the sound/vision carrier ratio. With this arrangement, 100% sound modulation depth is not a problem, in fact it will go beyond 100% (inverted carrier)! This is because the peak sound power on 405 should be equal to the peak white vision power, but the modulator when working with negative mod, has more than peak white to sync tip range (as peak white is 20% carrier).
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Hi David,
Sorry,I don't agree. I think there is a confusion with modulation depth and sound/ vision carrier ratio. These are different and independent things.
If you use the vision input for sound and switch the IC to negative vision mode (means PAL vision mode SYSL=0) you'll get something between 76% and 88% typical 82% modulation depth.
If you use your bias pot for the sound/vision ratio adjust it will be lower.
There is a biasing for maximum modulation depth, the sound/vision ratio adjust must be made with the output adding resistors.
Kind regards,
Darius