Total posts : 45366
I am also having a similar 120Hz hum problem. However, I have my matched AM antenna inside. I notice that the hum recedes and is nearly eliminated when the radio is near the antenna and gets worse farther away. I have used a battery to power the transmitter, with the audio input disconnected, to see what happens with a totally isolated system. I still get the hum. I have not yet attempted to shut down circuits, so I will see if I can isolate the problem to a particular circuit.