The extra length of the VHF cavity used for the 220MHz duplexer should do nothing to the tuning, insertion loss or notch depths. I suspect there may be another issue with your observed results.
Did you measure the poor performance without tightening or inserting ALL the screws on the top plate? I know for a fact that the length will not effect the performance of the cavity once the length of the resonator bottom is beyond the capacitive tuning effects. There is no effect of the bottom cover/cap except for dust protection. Harold (ex Sinclair systems engineer) --- In Repeater-Builder@yahoogroups.com, "holycow619593" <[EMAIL PROTECTED]> wrote: > > I've noticed that without reducing the size of the cavities, the depth > of the notches would only reach 60dB. When I reduced the length of > the cavities with a block inserted up the bottom of the cavity, the > notch achieved 80dB and the insertion loss dropped from around 3dB to > less than 1.2dB. > > I've read on a number of posts others have found the length of the > cavities didn't matter. As a test, after tuning the modified > duplexer, I tested the unit on a service monitor with a 50W repeater. > > The receiver desense on TX was well in excess of 6dB, indicating a > lack of isolation after tweaking the trimmer capacitors. Upon > reducing the cavity length and slightly retuning the notch points with > the capacitors, the duplexer now exhibited 85+dB of isolation, and no > appreciable desense on transmit. As a seasoned commercial tech with > many years working on Sinclair products, I found that until I reduced > the cavity length, the duplexer would not achieve spec. > > Does anyone have the length of the coupling loops for the Q2221E? >
