I recently built this mic amplifier circuit (source):
The output is connected to a speaker, but it's not exactly working as intended: I can only hear myself at the output if I blow hard into the microphone, otherwise not much. However, when I touch the metal casing of the microhpone, it behaves like an antenna and broadcasts what seems to be an AM signal from Quebec. This is fine, I understand that the mic can behave like an antenna, but why does this happen only when I touch it?
I noticed this quite a bit with electronics, particularly when there's transistors involved that touching the electronics has an effect on its behaviour, why is this?
It's also interesting that putting the mic into contact with other insulating materials like my desk or paper has no effect, but only with skin contact in particular it seems to make a good antenna.