|
Often it's the RF modulator that causes the buzz (especially if it's a consumer grade modulator). Many modulators have crude automatic level control, and the carrier gets cascade AM modulated (by video) and FM modulated (by sound). When that's the case the video AM modulator will modulate over 100%. When that happens the RF carrier will change phase 180 degrees(which is BAD). Phase modulation and frequency modulation always happen together and thus will both be demodulated by an FM detector. It creates a 60Hz buzz because video repeats due to frame rate at 60Hz.
A solution (my preferred solution) is to use a professional grade modulator like a Blonder Tongue AM or BAVMz series which has manual video level control that can be set to stop overmodulation of the video carrier.
|