I have been scouring the internet trying to find this answer, I've found hints and ideas, but nothing concrete, like an actual theory of operation.
I'm making a fox and hound wire tracer for my final project in ECE 202. The signal generation isn't hard, I get that concept, but I'm having trouble figuring out the theory behind the "hound," that picks up the signal from the wire.
I had always thought they used inductance to pick up the signal from the wire, and found one such design here. I may go with that, but I still want to know how the more common (and likely less bulky) capacitve probes work.
I found these three schematics, all of which seem to be a variance on the same principle. I see a capacitor connected to a high impedance before going into the amplifiers. The fancier ones appear to have some sort of bandpass filtering circuit as well, but I know what to research there.
I just don't understand the principle which is allowing these to pick up the signal.
Is it just an antenna? If so, what is the purpose of the capacitor? I vaguely recall something about electrically lengthening an antenna with inductors and shortening with capacitors, but that doesn't seem like what's going on here.