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Setting and Maintaining Modulation Levels

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1 Author(s)
Farmer, J.O. ; Scientific-Atlanta, Inc.

We deal here with two related problems faced by the user of television modulators: the problemn of initially setting modulation and the problem of maintaining it over a long period of time. Actually, we have four problems here, because the same problems exist for both audio and video. Failure to maintain correct video modulation may result in loss of sync, a washed out-picture, and weak color in the case of undermodulation. Overmodulation can result in poor detector, amplifier, and kinescope linearity, causing problems with the intensity and tint of picture highlights, and can cause excessive sync buzz in the audio channel. Undermodulation in the audio channel results in weak audio and poor signal to noise ratio. Overmodulation of the audio can result in distortion. Any errors in setting modulation levels are particularly annoying when changing from one channel to another. Signal processors will generally not alter the modulation level of off-air stations, though frequency response errors will cause an apparent change in video modulation depth at higher video frequencies.

Published in:

Cable Television, IEEE Transactions on  (Volume:CATV-2 ,  Issue: 3 )