1. Unharness all cavities
That's the only one you got right ?
After unharnessing, the first thing you do is set the coupling to the desired or spec¡¯ed insertion loss. For a bandpass cavity, each loop has to be set such that the return loss is identical in both directions (S11 and S22).
As you adjust loop coupling, the resonant frequency is going to move around, so you have to do this first, not late in the game. Also, the return loss is going to vary with coupling. The tighter the coupling, the less insertion loss there will be, and the better the return loss will be. As you loosen the coupling, the insertion loss goes up (and so does the Q), and return loss degrades. A properly-operating bandpass cavity will typically yield 20 dB of return loss when the coupling is set for 1 dB of insertion loss ¨C you can use that as a sanity check.
At the risk of repeating myself, it is imperative that S11 and S22 be identical. If you don¡¯t have a VNA to do this, you¡¯re going to spend/waste a lot of time swapping cables around and going back and forth between the two loops iteratively until you get it right. So, unless you know that somebody has messed with the coupling, or if you see S11 <> S22, you may not need to even touch the coupling.
Once the coupling is set, then you tune them for the frequency of interest based on the best return loss. The harness everything back together and check that it makes spec. If everything was done correctly, and the cable lengths are correct, you should not need to do any "touching up".
6. Set notches on each pass
How would you have notches in a bandpass duplexer??!?!?
--- Jeff WN3A
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