What is radio static? Why isn’t there just silence in the absence of a broadcasting signal?

Question

What is radio static? Why isn’t there just silence in the absence of a broadcasting signal?

In: Physics

Answer 1

Radios have automatic gain control (AGC) in their circuits that process radio signals. They turn up the amplification until there’s a strong enough signal to process. If there’s no radio station then it will go to maximum amplification and you’ll hear partly radio noise, partly electronic/thermal noise from inside the radio. The volume control on the radio affects only the audio amplification but the AGC operates on the radio frequency side.