How true you can also tune duplexers using a receiver, but you need a signal generator. I would ask if anyone local to him has the gear to check his setup, you can spend a longgggg time playing with duplexers without the right test gear, I know from experience. The other thing is insertion loss Yes you do need to use good coax and decent connectors
73 Steve ----- Original Message ----- From: Tim Sawyer To: [email protected] Sent: Friday, May 21, 2010 4:17 PM Subject: Re: [Repeater-Builder] Duplexer on the cheap worries 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 <[email protected]> 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 To: [email protected] 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 <[email protected]> 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
