I realized a problem with the AGC design I talked about: The output impedance will vary a lot with gain. I'm not sure how much of a problem that is, I guess it depends on what it's driving, but it's definitely an issue. I'll have to simulate that.
Another question on that: the input to that MOSFET is obviously going to be high impedance, but it's coming from a filter that's going to be low impedance. (high impedance LC filters don't seem to be feasible). Normally you would put a resistor to ground to terminate the connection, but then you are introducing noise. Is that an issue? Since the frequency is fixed, could you put an inductor of the right value there?
Also, Bob, you mentioned building boards for testing. How do you do that? Do you put a zero-ohm resistor between sections and an SMA connector on each side of it? You probably want some way to enable power per section. Anything else I need to worry about?
As far as building boards, getting the board itself isn't that expensive, but how much does it cost to populate the board? The processor is a BGA; I'm not sure I can solder that, and having someone else handle all the soldering would be nice.
Also, there's the signal generator you mentioned. I found a couple, like https://www.amazon.com/Seeku-WB-SG1-Signal-Generator-1hz-8ghz/dp/B082WBZ9S3 but I'm not sure which you are talking about.
Thanks,
-corey