Posted 20 August 2010 - 06:28 PM
re: PAL 50Hz videocams used in NTSC-M 60Hz countries
A commonly seen problem is the AC beat 60-50Hz = 10Hz which shows up in the screen as a (slightly brighter) wide bar slowly scrolling (up or down). This is independent of if any device (including the TV/video monitor) is AC powered or not. If using AC power, the interference is even more severe. Without AC supply, it has something to do with the "grounding coupled signal". Very often the ground will influence/inject the 60Hz sine wave (if NTSC countries) into the signal path.
P.S. the ground is not 0 volt potential. It is also connected to the Neutral (the White-colored wire) in the house power panel as well as in all power distribution substations and power plants.
P.S., sometimes you can even hear the harmonics of 10Hz if the volume is not lowered.
P.S. the story is also true if using 60Hz videocams in 50Hz countries