> The cavities were initially tuned individually and the loop
> positions set for
> 1 db IL. They were then coupled together using a 18.5" cable
> and the rods
> touched up to re-establish resonance.
If the cavities had good return loss individually, there shouldn't be a need
to "touch up" the tuning when they are cascaded. That's what I was saying
originally with my "detuning" comment.
> The loop
> positions were not changed after coupling.
But were the loops adjusted to maximize return loss at the desired
inseretion loss setting? That's the key point. Or did you just "dial in" 1
dB of insertion loss and call it good?
> When using the RL
> bridge I do not
> see one clear notch, but rather a notch that has a bump;
> kinda looks like 2
> notches.
Again, this may be indicitive of them not being tuned correctly.
> This is what I always see even when cavities are
> factory tuned
??? There's no acceptable generalization when it comes to how cavity
filters behave when cascaded. Two cavities used as a window filter with an
extended passband will look different for both transmission and reflection
than would two cavities tuned (and cabled) to pass a single frequency.
> I'm confident that the tuning is OK.
I wouldn't be so sure, as it seems likely that's the problem.
--- Jeff
