Thanks for the input. The original failure came from a bad connection of the output strap.
But I do agree the duplexer has become detuned. I am just not wanting to touch it because it has most likely not been adjusted in 25 years, has rust on the tuning rods, and we are involved in an RF design contract to replace the whole shooting match. So far reducing the power out to 25 watts has seem to have cured my problem so far, and no input from the users of decreased coverage. So, as long as I can get by for now, that is my goal. -Tim ----- Original Message ----- From: "Eric Lemmon" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, April 24, 2004 7:17 PM Subject: Re: [Repeater-Builder] To adjust or not.... > Tim, > > I suspect that your amplifier failure came about as a result of the > duplexer being detuned. Even the best duplexers can gradually drift due > to a phenomenon called "rod pumping." This is far more pronounced at > sites where the duplexers are not in a temperature-controlled > environment. But, even in an air conditioned building, normal operation > of the duplexer causes significant heating. A typical 4-cavity duplexer > might have a 1.5 dB insertion loss, which means that a 100 watt > transmitter will lose around 31 watts in the duplexer. That amount of > heat in a high duty cycle repeater can make the cavities too hot to > touch. Despite the presence of Invar rods, the continuous cycling of > temperature will, over time, cause the duplexer to creep out of tune. > > Let's not forget that the notch moves with the bandpass in a "BpBr" > duplexer, so the extremely important notch in the TX side that protects > the receiver from transmitter sideband noise is slowly becoming less > effective over time, causing desense to appear. Because the system > deterioration happens so slowly, it seldom rears its ugly head until > something breaks or the users complain about poor coverage. > > The PA failure might have been coincidental, but I would give the > duplexer, isolator, feedline, and antenna a good going-over. I believe > that this inspection should happen on a regular basis, at least every > two years. > > Tim Shephard wrote: > > > ...Lately we have been having some trouble which has been nicely termed > the whale noise. ...Yesterday I checked everything and found I was > getting some desense, around 8 dB... I looked at the duplexer and it > looks like it has not been touched in around 25 years. The shafts are > rusty, cables look very fragile... What do you guys think? > > > > > > Yahoo! Groups Links > > > > > 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/
