Ok, if they are the type with the variable coupling loop you should have 2 coupling loop holes per cavity, just one has a round hole cover. If so take 2 cavities and transplant a coupling loop to one of them to make 1 band pass cavity. Make another one for the RX side
Place the band pass cavities closest to the repeater in each leg. So you have 1 band pass and 2 rejects and then the tee. If that doesn't work you might try converting them to BpBr. This would be done by adding a very high quality piston trimmer such as a johansen cap to the coupling loop, in series with the grounded end. Or a BNC jack going to a piece of coax that can be trimmed to form a gimmic capacitor. I like to salvage the capacitor from surplus Mastr 2 ICOMs that are EC. But those have to be soldered in and I'm not sure what material DB cans use on the rotatable whosis. The inner cavity jumpers should be 1/4 wavelength electrically, so you have to calculate velocity factor of your cables. 4 cavities should give you 80-85dB. and I like to use a circulator as the tee to the antenna which brings it up to the 100dB range.. But if you don't have one, try just 4 cavities and if you still have desense try 6. On Mon, Aug 10, 2009 at 10:21 AM, tahrens301<tahr...@swtexas.net> wrote: > Hi Dcflu7x, > > It's a DB products SP-1894. Can't get any info on it from > anywhere. > > Each of the 8 cans have the approx dimensions of 5" x 21". > A single screw-type shaft in the center, and one SO-239 > sticking out of the top of the can. No variable caps, or > anything else on the cans. Each can has an RG-9 jumper > between each 'T'. The male portion of the 'T' screws down > into the can. > > The 4 cans on the 147.7 side are strictly 4 cans in series. > The 4 cans on the 147.1 side also have an additional 'T' > between cans, and from that dangles a short stub. > > The stubs actually pull up the high side of the notch. Without > them, the cans exhibit high loss at 600khz above the notch. > With them, the total loss is about 2 - 2.5dB. > > The duplexer was originally in the 166 range, then pulled down > to the 154 range, which was what they were set for when I got them. > > Tuning: First I used the spectrum analyzer with tracking generator > to move each notch on top of each other at the desired frequency. > Next, I used my service monitor to generate a +10dBm signal > which I fed through each set of 4 cans. On the opposite side, I > hooked up the spectrum analyzer & tuned out the signal. It told > me it was between -92 & -95 dB on each set of cans. I also put > a 50 ohm load on the port that I was not testing. > > I think they are tweaked as good as they can be. > > Thanks, > > Tim W5FN > > > > > --- In Repeater-Builder@yahoogroups.com, DCFluX <dcf...@...> wrote: >> >> Can you tell us more about the model of your duplexer? >> >> When you say notch is it: >> >> A. Flat pack mobile style notch only duplexer with a 3MHz minimum split. >> B. Wacom BpBr cavites such as WP-639. >> C. Motorola style notch only small cans. >> >> Also if you have a VHF circulator you can replace the tee between the >> 2 sides of the duplexer and antenna for an additional 20dB of >> isolation. >> >> >> On Mon, Aug 10, 2009 at 9:07 AM, tahrens301<tahr...@...> wrote: >> > Was just curious as to if folks have >> > gotten Notch cavities to work ok with a 600khz >> > split. Have 4 in Rx leg & 4 in TX leg. According >> > to the analyzer, each bank has a >90dB notch. >> > Double shielded cable throughout (RG-9). >> > >> > Just about pulled all my hair out over the last >> > couple of weeks, and still have desense issues. >> > Even tried another repeater, just to see if it >> > was still there, & yep it is. (was actually a >> > bit worse than the Quantar, but it uses cheesy >> > cables for RX (TKR-720)). >> > >> > Did find something interesting inside the Quantar >> > tho, the RX cable that screws into the RX filter >> > housing had a problem. They use a crimped Mini-UHF, >> > and the section that got crimped actually rotated >> > freely around the piece that has the center conductor >> > in it. Nice rotatable cable, but don't think that >> > it was intended to do that! Soldered the two together. >> > >> > Thanks, >> > >> > Tim W5FN >> > >> > >> > >> > ------------------------------------ >> > >> > >> > >> > Yahoo! Groups Links >> > >> > >> > >> > >> > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > >
