Quote:
Originally Posted by electroking
I think the answer is not that much related to sensitivity. Your typical 5-tube radio
has enough gain to amplify the atmospheric noise to an uncomfortable level.
The advantage of a tuned RF stage is improved rejection of the image frequency,
which is useful when the band is open, or when you have a local station at or
near the image frequency of the weak station you are listening to. The image
frequency is 910 kHz above the actual setting of the dial. For instance, if
you set your radio for 660 kHz, you may be able to hear a station transmitting
on 1570 kHz. The RF stages will amplify much more at 660 than at 1570
under such conditions, thus improving the performance.
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You are confusing sensitivity with gain. In the context of a radio, sensitivity means how much signal the radio needs at the input for a given signal to noise ratio at the output. This is why a more sensitive radio is more capable of receiving distant broadcasts than a less sensitive one.
If gain were the only measure of sensitivity, it would be quite useless, as you stated above.