As you know, a radio uses some kind of freqeuncy-selective filter to selected the wanted station from all the others. And it then amplifies that signal. But since all the different signals have different strengths when they reach your radio (and a particular signal may even vary in strength), you'd have to keep on adjusting the volume control as you were tuning the set to ensure that (a) you didn't miss any signals and (b) you didn't drive everyone mad when you hit the stronger signals.

So all modern radios (the idea was first used in the 1930's, I think) have a circuit called an Automatic Gain Control (AGC) [Sometimes called Automatic Volume Control - AVC - in older books). This circuit measures the average level of the received signal and adjusts the gain (how much the set amplifies the signal) so that all signals appear to have the same volume. Weak signals get amplified more than strong ones. Now, firstly static is always there, even when you're listening to a strong station. Don't think it's stronger when there's no station - it's not. But if there's no station, then the AGC circuit makes the set amplify the (non-existent, really) signal as much as it can, so the (very weak) static sounds quite loud Secondly, by measuring the control signal that controls the gain you can get some idea of how strong the signal is. The less gain the radio is using, the stronger the signal. That's almost certainly what the meter on your radio is measuring.

Yes. Unless they detect a suitably strong signal, they'll skip over it. A real pain if you're trying to receive a very weak signal. -tony

from the couch if I want to change anything. Gives me some exercise. :^))