Effects of AM-to-PM Conversion of TV Transmitter on Video Signals

Incidental phase modulation caused by AM-to-PM conversion (carner phase shift) of RF amplifier degrades the detected video signal performance. Its effects are known to be different for different types of demodulators as well as for different signal types to be incidental phase modulated. This paper shows a simple and general analysis for any form of AM-to-PM conversion using derivative form and supposing the video signal to be relatively small. From the analysis, it can be seen how the video-to-video frequency response varies and how much of the lower sideband (LSB), once filtered, will emerge with respect to the amount of AM-to-PM conversion. The general equation to predict the differential phase (DP) and differential gain (DG) degradation caused by AM-to-PM conversion is presented, from which it is shown that there are special AM-to-PM conversion cases that cause no DP and/or DG degradation.