I used to buy and do light repairs to shortwave and AM radios. A relic of that time is that I have an "isolation transformer", a 1:1 transformer to isolate the

I used to buy and do light repairs to shortwave and AM radios. A relic of that time is that I have an "isolation transformer", a 1:1 transformer to isolate the radio from ground. 110 in, 110 out.