Quote:
Originally Posted by lowedb
However, I've just spoken to our antenna Engineer, who had been told the same, but he did some digging, and it seems you are right that it's not as I (or he) believed. However he tells me that it's not the IF at a varying level either (he had a scope on it and there was no RF. He tells me that its a low level signal at close to DC. I can only assume it is a voltage corresponding to signal strength. Sorry if this is getting a bit deep.
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That will be an amplified AGC output. Basically a radio tunes to a signal, the IF output of which is converted to a DC voltage which is then fed back to the RF stages to control the amount of gain - called AGC or automatic gain control. So the AGC voltage depends upon the received signal strength of the station it is tuned to. Tune to a weak station - the gain is turned up to improve the strength, tune to strong station and the gain is turned down. That AGC voltage is also fed into the diversity amp, which can then try either of the two antennas, to see which provides the stronger reception for the station you are tuned into.
On a rather more specialised radio set, the AGC voltage might also be fed to a meter, to give an indication of the signal strength of a received signal.