I built this "AC Mains hum detector" circuit and
the yellow bar is just a piece of copper wire (about 20cm). When you put the antenna near a mains ac source line the led lights up. Question is why does this work? What I am confused about is that the first transistor is obviously 'on' when the EM field interacts with the antenna, but I cant measure the voltage at the base without disrupting the thing and it turns off. Is it the electro-part inducing a voltage or the magnetic part making a current (or both?). The other thing that is bothering me is that the base is "floating" and i don't really have a way to describe this. Thanks for the help