Guys, Thanks for the replies. I guess once I downloaded the manual and studied the cabling diagrams, I now understand what you all were saying about the cables attached directly to the cavities. The original cables were 11.5 inches on low side, and 10.5 inches on the high side. The high side tuned fine (pass & reject), but the low side's reject would not pull to the high side of the pass frequency.
I added a few M-M and F-F barrel adapters to lengthen the cables, and the reject tuned perfectly. My cable lengths with the adapters ended up being around 12.5 inches for the low side. A little longer than what the Sinclair notes called for. Being the original cables were made from RG213, which in my opinion is a no-no with duplexers, I decided to make two new cables out of RG393 thermax double silver shielded cable. I first tried making the cables the length above of 12.5 inches, but the cables turned out to be too short. Same results as the original RG213 10.5 inch cables. Added the adapters back to the new jumpers, and tuning was good again. I then made another RG393 jumper about 15 inches, but then it was too long, and the reject tuning rods wound up being out too much. I then shortened the cables to 14.25 inches, and the rods tuned perfectly. I then made two more cables for the tx(high) side, but once again, too long, so I needed to shorten the high side RG393 jumpers to 13.25 inches. I'm guessing the RG393's velocity factor is the issue behing the cables having to be physically longer than the RG213 cables for the same frequency. Thanks again for all the suggestions. Eric KE2D --- In [email protected], [EMAIL PROTECTED] wrote: > > 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. >
