I was afraid of that.
In short, you can't have an AGC circuit in a wideband RF amplfier. Well you can if you want, but you probably won't like the results.
The issue is when you're listening to a weaker station at 90.1 MHz (for example), and you drive past an extremely strong station at 107.1 MHz (for example), and the antenna AGC backs off the antenna gain making the desired signal sink into the receiver's noise floor.
With AGC circuits, it's critical to ensure that the feedback signal is a product of the desired signal, AND ONLY the desired signal. And this means that the feedback control signal must be derived from the filtered IF signal within the receiver.
Even with IF-derived AGC, it's considered to be a receiver flaw if the receiver desensitizes due to signals that are close enough to affect the AGC, but outside the narrower downstream IF and AF filters. The operator is left wondering why the receiver is desensitizing. Good receivers take extremely measures to minimize this issue.
The better approach is to ensure that the antenna amplifier provides only minimal gain (proper gain distribution), and provides an exceptionally wide dynamic range (low noise combined with high limit for linearity).
There may be a moderate amount of antenna AGC that would be operationally acceptable. Where the designer assumes that the user is not likely to be listening to signals very close to the noise floor. But then one might as well reduce the antenna gain by that fixed amount. Otherwise the gain will go up and down seemingly randomly.
