I recently wondered the same thing about a Phelps Dodge six cavity duplexer here. I found that all six cables including the two to the tee connector were the same length: 8-3/4 inches tip to tip on PL-259 connectors. (<http://repeater.w4zt.com/duplexer/>)
The problem here was noise, lots of it, and anytime one of those cables was moved even slightly the noise became much worse. These original cables were made from PDC's own house branded RG-8 cable and supplied pre-tuned on 146.625 MHz. I decided to replace the cables and assumed the same thing that Eric pointed out below, whatever length works, and the base assumption "minimum length to fit" worked for me. I replaced the house branded RG-8 with jumpers I made from Andrews FSJ1-50A 1/4" Superflex Heliax. I realized the VF was greater but shorter cables wouldn't reach so I made them the same as original. Details of my superflex to PL-259 connector project are here: <http://repeater.w4zt.com/duplexer/superflex/>. After completing the superflex mod I also welded up a bracket to hard mount the tee connector. I reassembled the harness and checked the duplexer. It was back to spec and NO NOISE! Move them, bang them, shove them, no effect. Problem solved! In this case, the difference in cable length made no measurable difference in performance but the move to the 100% shielding of the superflex heliax made a huge difference. If you're making cables, I would highly suggest you consider making them from the superflex heliax so you can completely eliminate the leakage and noise problems from your duplexer. 73, Tony W4ZT At 12:33 AM 10/13/2004, you wrote: >Neal, > >The best answer to your question is probably: Whatever works! Both Bill >Lieske of EMR and Len Pringle of Telewave have given me pretty much the >same answer about jumper lengths for duplexers they manufacture. > >In most duplexers, the cavities are individually tuned for the desired >insertion loss by adjusting the coupling loops or probes, and each >cavity is tuned for the desired pass loss and notch depth. This is an >iterative process, and eventually the technician has two or three high >pass cavities that are identical, and two or three low pass cavities >that are identical. > >At this point the technician selects a test jumper from a rack of >pre-made jumpers that are arranged in 1/2 inch (usually) increments. > From long experience, he picks one that he knows is close to being the >right length. If each cavity had 0.6 dB insertion loss, he looks for a >jumper that results in about 1.2 dB loss for the pair. If the loss is >more than 1.3 dB, he'll try a shorter or a longer jumper until he finds >one that gives the minimum combined loss. If this is a six-cavity >duplexer, he'll add the third cavity and repeat the process, looking for >about 2.0 dB total loss. If the customer wanted a deeper notch, each >cavity's loops might have been set for a different coupling, which means >that the optimum jumper cable lengths might not be the same. So, the >jumper lengths are not always pre-calculated. > >Some duplexer manufacturers have just two or three cable harnesses that >they use for all duplexers in a particular band, and these are >compromises. Sad to say, many commercial installers have no interest in >optimizing their installations, because that effort is time-consuming >and is therefore costly. Hey, if it works, that's good enough! A >purist does not embrace this one-size-fits-all approach! > >Regarding jumper cables, they should always be double-shielded; RG-214, >RG-142, or RG-400 are good choices. Do not use RG-58, RG-8, or RG-213 >because those are single-shield cables. > >73, Eric Lemmon WB6FLY > >Neal Newman wrote: > > > > BTW the cans are WP-641's > > > > Neal Newman wrote: Hey Guys.. I am having a problem with my Wacom > Cans... I am just curious what should the length be for the 4 jumpers.. > the 2 between the cans and the 2 that meet at the output Tee..... the > repeater is on 145.230 and what type cable should be used ( I think it's > RG-213?) I noticed that one cable is teflon... and 2 seem longer than the > other 2.. I tookmMeasurements.... the jumpers between the cans measure > 8.5" and 8.75" the 2 jumpers between the cans and the output tee measure > 11.77" and 13.5 "(teflon) I know this is not correct... Serves me right > for loaning out the cans to friends club for a few years. For some reason > I always thought all 4 cables should be about 13" but I may be wrong... > Does anyone know the correct length? BTW I measured tip to tip of the > pl-259's Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
