Joe--- If what you say is really true about having no desense when you are terminating your duplexer into a dummy load, your problem is most likely from there on out into the antenna system including the possibility of your transmitter mixing with something that is there when you are or some new corrosion rectification is another possibility----your feedline connectors or antenna or tower structure somewhere close.
But before you can say that you have no desense into a dummy load you have to do a real weak signal test. This is because wide band noise, like comes out of a bad duplexer from internal micro-arcs, when the transmitter is on, is usually indistinguishable from no signal receiver noise if all you are doing is listening to the receiver. Said another way, you can have really bad desense noise from a bad duplexer and not be able to hear any change in receiver output noise when the transmitter is switched on and off. You have to do some real testing to be sure. The simplest test is to put an iso "T" in front of the receiver input. With the transmitter off, inject a qualifying signal into the "T" with a couple of kc. deviation. When you get things working, reduce the injection signal to where you can just hold your repeater open and then turn on your transmitter----if and only if you have no desense you will not hear any change. If your test signal goes away, increase the injected signal level until you get back to the transmitter off apparent signal to noise ratio that you started with. If you are able to measure how much you had to raise your test signal when your transmitter is on, that is the amount of desense your duplexer is ----for some reason ---leaving you with. Scott ----- Original Message ----- From: jminn699 To: Repeater-Builder@yahoogroups.com Sent: Monday, October 01, 2007 8:25 AM Subject: [Repeater-Builder] Re: Duplexer and noise question -I am having the same problem also with a wacom duplexer. On a dummy load the tunning checks great with no desense, but with the antenna attached the repeater will hang on transmitting noise as long as the ttansmitter is on. I can`t take the system off the air, and I don`t have another duplexer. My short term solution has been to set the repeater hang time to zero. Another would be to make the tx pl different from the rx; but I am hoping to avoid reprogramming all the radios on the system. My system is located in a lousy enviorment, a elevator equipment room-there is a layer of carbon dust on everything. I suspect that this dust may have found its way inside the cans, but I can`t take it off the air to open up the cans. I hope someone has a solution to this problem. Joe -- In Repeater-Builder@yahoogroups.com, "Dan Cation" <[EMAIL PROTECTED]> wrote: > > Hi everyone - new to the group looking for help on a strange problem. > I've been involved with two repeaters in Southeast Kansas (Humboldt - > 147.18 and 442.900) for over 30 years and work in Electronics, > although not in radio. A couple months ago we lost both repeaters > when we had a flood in this area - I took the Wacom duplexer apart and > cleaned any obvious corrosion or such and assumed it would be fine - > it tuned up without any trouble and there was almost no corrosion. I > replaced as many of the T connectors as I could and carefully cleaned > any that remained and made new cables of the correct length. I have > built a new repeater but am now having a problem with intermittent > buzzing sometimes when the transmitter is up - it will hold the > receiver open and cover any signals that aren't pretty strong. Comes > on whenever the transmitter comes up but not always - sometimes it is > fine. I have tried 3 different transmitters - a Midland 3400, a > Midland 340A and even a couple Icom rigs - makes no difference. Same > for receivers - makes no difference. Never shows up unless the > duplexer is hooked to an antenna - works fine on a dummy load. Tried > two different antennas as well. The noise sounds like bad line noise, > but I can't hear it except on the repeater. The repeater is at my > house right now, but I intend to haul it back to the site to see if it > shows up there as well when I can get time to do it. Anyone else ever > ran into this kind of thing? >
