When the amplitude of the RF signal becomes small enough, the RF receiver will seem to start amplifying more of the noise on the antenna. You'd think the noise amplitude would always be small and the signal amplitude would just get smaller and smaller until it was equal to the noise amplitude. But this doesn't seem to happen, as the signal amplitude weakens, the noise amplitude seems to get larger. Why is this?

Thanks

 

The noise amplitude AT THE INPUT will be more or less consatant but if you tune to a week signal the AGC (Automatic gain control.) will increase the gain of the IF amplifier (And possibly the RF amplifler.) so the noise level at the detector will increase.

Les.

 

Oh ok, automatic gain control is what i need to know. Thanks!