Yep, low isolation in the duplexer could be the problem. And the correct thing to do is measure it. But if he doesn't have the test gear putting a dummy load on the output of the duplexer will give a pretty good idea whether the duplexer is tuned correctly or not. If there's no desense with a dummy load then the RG-8 might be the problem.
On Fri, May 21, 2010 at 7:59 AM, Steve <steve.m1...@tiscali.co.uk> wrote: > > > Hi Tim > see my message, you really do need to check isolation with an analyser > I had a look at a duplexer for a chap and there was just 30dB isolation so > needless to say the desense was tremendous. It took an input signal of > around 70 microvolts to overcome desense. I retuned it on my analyser > and got >80dB and it worked > > Steve > > ----- Original Message ----- > *From:* Tim Sawyer <tisaw...@gmail.com> > *To:* Repeater-Builder@yahoogroups.com > *Sent:* Friday, May 21, 2010 3:47 PM > *Subject:* Re: [Repeater-Builder] Duplexer on the cheap worries > > RG-8 is not good for duplex. The braid will make TX noise and get into the > receiver. Cheap antennas can make the same problem. Test into a dummy load > right at the duplexer. If no noise then you know it's the feed line and/or > antenna. > > 6.5 inch dia cans are big ones so you should have plenty of isolation > specially for 2 watts. > > On Fri, May 21, 2010 at 7:28 AM, kc0mlt <kc0...@yahoo.com> wrote: > >> >> >> Hello all. >> >> I am trying to figure out if the duplexer we have put together is up to >> the task or not. Here is the situation. We have four cavities 6.5" dia. one >> is a vari-notch the others are simple reject cans. Two rejects are on the TX >> side and one reject and the vari-notch are on the RX side. All set and tuned >> with rg-213 jumpers between cans and RG-142 from the cans to the Tee >> connector. We are doing some light testing with a cheap dual ban antenna on >> the garage. It is feed with RG-8 about 70 feet. We are having some issues >> with receive. It kind of sounds like desense but I think it is something >> wrong with the receiver. I was just wondering if the cobbeled together cans >> sound like thay are doing a good enough job as a duplexer or if we do have >> something to change on it. The repeater is only putting out 2 watts for >> testing. I would think I have enough separation for that power level. Any >> suggestions or thoughts woyuld be greatly appreciated. >> >> Thanks >> Wade >> KC0MLT >> >> > > > -- > :wq > Tim > > > -- :wq Tim
