> Jeff,
>
> But for the purpose of this exercise, setting the loops, the
> position of max RL has to be the position of min. IL? No?
That's what I said in #7. After you've tuned the cavity to resonance based
on RL, you check the IL. The frequency of the RL maxima (dip) should
coincide with the insertion loss minima (peak) if everything is done right.
> I've never used an RLB to set the loops; I've always used an SA/TG.
Like I said, you have to use the SA/TG to view the transmission response in
order to quantify how much insertion loss you have, and that's why I
suggested you "rough in" the insertion loss initially, and, if necessary, do
a second round of tuning if you find, after all's said and done, that the
final measured insertion loss is too far off your original target.
To say it another way, you coarse-tune the loops targeting your desired
insertion loss, then you fine-tune looking at return loss.
Note that everything I'm telling you is how to tune up a single cavity.
Once you have the two tuned up independently, go ahead and connect them
together and report back the results.
> I also have several different tutorials on cavity tuning, but
> none even touch on the IL adjustment.
I think a lot of manufacturers assume that the field tech has no way of
measuring return loss (either with a SNA, VNA, or SA/TG+RLB). So, they put
those little stickers near the loops with index marks that indicate
(sometimes vaguely) where the loops need to be set to achieve the desired
insertion loss, and they assume that the return loss will come out "close
enough for field work".
--- Jeff WN3A
