Linley F. Gumm

Phase Effects in Cross-Modulation

CATV amplifiers can convert amplitude cross-modulation into phase cross-modulation. It has been generally assumed that this is desirable. A theory is developed and checked experimentally that shows that the fm deviations caused by the phase shifts are visible in television receivers. If the phase shift exhibits a rise time of about 100 ns or less, phase cross-modulation and amplitude cross-modulation are equally visible if the sidebands of the two modulation processes are equal for a 15 kHz squarewave. The visibility of the phase cross-modulation is rise-time dependent, showing a 12 dB decrease in visibility as the rise time is lengthened to about 300 ns.