I am a test engineer at IC company doing some work on a satellite switch. I need to test the chip using DiSEqC and tone/voltage. First, what is tone/voltage control? I can not find any information anywhere. Second, I am trying to figure out why such a complicated way of signalling was created. Apparently somebody wanted to use a single coax to supply both power and control. Oviously if you have DC on the coax providing power, then the only alternative for control is to modulate the signal. This is done arbitrarily at 22KHz (or is it arbitrary?). So the question is, Does the 22khz tone ride on the VCC line, inductively coupled or something? When a non-22KHz state is desired, is the 22KHz signal just opened up? And what is the technique to reading back the DiSEqC commands from the slave? Is there some kind of envelope detector?