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. The measured IL is now 2.9. The loop positions were not changed after coupling. 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. This is what I always see even when cavities are factory tuned, so I'm confident that the tuning is OK.
On Tue, Apr 20, 2010 at 9:26 AM, Jeff DePolo <j...@broadsci.com> wrote: > > > > I have 2 C-Series bandpass cavities, with individual I.L. set > > at 1.0 db each. When I couple them together and measure, I > > get a total I.L. of 2.9 db. I should see something like 2.1 > > or 2.2. I have measured the coupling cable and see < .1 db, > > so the cable is good. Anyone have an idea why the loss is so > > high when coupled? > > Most likely they aren't tuned correctly for maximum return loss, and when > you cascade them, the resonant frequency is no longer where you thought it > was (i.e. a "detuning" effect). Have you measured the return loss of the > cavities individually? > > --- Jeff WN3A > > >
