The following is the response as traced by the Si application (previous post on unit #1 includes block diagram). The blue is the response of both sections while the gold (its faint) is a memory of the response with no filter attached. Not shown, is the unattenuated loop where the C-Aux is input to the B RF input directly yields a ~ -50 dB level. This indicates a roughly 8dB insertion loss.
There are a couple of issues going on here. First I could not get both filter sections to fully overlap - I always ended up with the double peak response. This may be due to over coupling between sections (need to go back and do some reading). The other issue is the roll off is not as expected for a two section filter. Part of the concern is the response without the filter (gold line). To investigate this, I used a spectrum analyzer to conduct a manual filter response. Those results compared to the Si results are below.
All in all this approach is better than previous attempts. Using 1/8" brass plate might sound nice and sturdy but it creates a lot of thermal ballast which makes soldering tricky. The material I wish I had read *prior* to starting this is from Sam Wetterlin. He has two documents far down the page that go into great detail on variations on cavity filter construction.