Eric, I had the identical issue with this duplexer. Eric Lemmon helped me solve the problem by commenting that the arrangement that Sinclair uses has a reject notch on both sides of the cavity resonance. A sweep of the cavity will show the two notches that can be moved in unison around the pass, with both notches moving the same direction as the stub is adjusted.
What you are missing is that the first piece of cable from each cavity to the Tee is part of the tuned circuit. My cavities were in the 170.xx range and the first cables were 10.5 inches. I increased the first cables from the cavity on the lower side from 10.5 to 12.5 inches and they tuned just fine in the ham band. Eric scanned the manual for my duplexer and I can send you a copy if you are interested. 73 - Jim W5ZIT -----Original Message----- From: [EMAIL PROTECTED] To: [email protected] Sent: Sat, 21 Apr 2007 10:31 PM Subject: [Repeater-Builder] Sinclair Q202 tuning problem I am having an issue tuning a Q202 duplexer. I reviewed the past 144 or so posts regarding Q202 issues, but haven't found any past posts mentioning the following issue. The unit was originally on 165MHz. It has the horizontal copper/dielectric reject stubs which screw into the T-box on top of the cavities. The target frequencies are 146.800 tx, 146.200 rx. The high side (tx)tunes just fine. I'm measuring about 1.5db insertion loss and 80db rejection on the tracking generator. The low side is the issue. The pass (146.200) tunes just fine, with 1.5db or so of insertion loss, but reject is an issue. The cavities on the low side act as if they are another set of high-side cans. The reject rods appear to tune properly, and I can get 80+db of rejection 600KHz low of 146.200, but no matter what I do, the reject will never go ABOVE the pass frequency. I doubt the cable harness lengths would cause this, no? From the past posts I read, it sounds like if I were running out of room on the reject rods, then the cable lenghts might be the issue. But my issue is that the low side's reject is sitting below the pass, not above the pass where it needs to be. The duplexer swept ok before I started retuning it. Any ideas? Would being an inch or so short on the L cables at the new frequencies really cause the reject to be on the wrong side of the pass, just on the low side only? The high-pass side tunes fine, allthough the clear rods are only out of the copper tubes by about 1" or so. Thanks Eric KE2D ________________________________________________________________________ Check Out the new free AIM(R) Mail -- 2 GB of storage and industry-leading spam and email virus protection.
