We had a similar problem years ago with a six meter repeater in Virginia. Problem was the site did not have a good ground and static would build up on the tower and antenna and cause all kind of noise on the receive signal. At first thought it was desense. Very difficult to get a good ground system on the mountain top.
David -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Chuck Kelsey Sent: Thursday, December 25, 2008 11:35 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Six Meter Repeater Noise Issues If it's power line noise you can check by keeping your TX off and have someone with a noisy signal key up on the repeater input while you listen on the local receiver. You could use your signal generator into a whip antenna. You'll know if there's something in there. You won't hear it without an incoming signal, by the way. Chuck WB2EDV ----- Original Message ----- From: Scott <mailto:sc...@becklawfirm.com> To: Repeater-Builder@ <mailto:Repeater-Builder@yahoogroups.com> yahoogroups.com Cc: Scott <mailto:sc...@becklawfirm.com> Overstreet Sent: Thursday, December 25, 2008 12:18 PM Subject: Re: [Repeater-Builder] Six Meter Repeater Noise Issues Tom I think you have a corrosion problem in your antenna system. I had a similar if not identical problem in a 2 meter repeater here----years of good performance and then serious desense. I ran the same tests as you have with same results. The fix here was an overhaul of the Hustler 144-G7 if I remember the numbers right. Corrosion was found in several places-----fix was to clean down to bare metal to bare metal and reassemble with no-ox in the joint and more under several layers of shrink tubing over the top for weather protection. The antenna is still in service with no trouble. Corrosion in the antenna results in transmitter signal rectification within the antenna which produces noise of sufficient bandwidth to cover your receive frequency and this of course comes back down your feedline and properly goes right through your duplexer into your receiver. The curious thing is that under most conditions, this wide band noise results in desense without changing the audio noise output from your repeater receiver when your repeater transmitter is switched off. The fact that desense goes away when the antenna is replaced with a dummy---I assume that you are injecting your test signal into you receiver using an attenuating "T"----I think your problem is your antenna or something very close by that it is exciting. Scott ----- Original Message ----- From: Tom Elmore <mailto:t...@telmore.com> To: Repeater-Builder@ <mailto:Repeater-Builder@yahoogroups.com> yahoogroups.com Sent: Tuesday, December 23, 2008 10:03 AM Subject: [Repeater-Builder] Six Meter Repeater Noise Issues Several months ago I put a six meter machine on the air in my area. It is a GE Master Pro tuned for 52.810 out and 51.110 in. One of the things still nagging me is some sort of desense or RF phase noise, let me explain. After tuning up the duplexers into a dummy load and running some tests I experienced no desense all the way down to about .15uV. I moved the dummy load to the end of the transmission line just to be sure and again the same results. When I put the antenna in line and run the same tests this is what occurs. When I key the transmitter and set the output of the signal generator from a starting point of say 100 uV I hear what sounds like phase noise or just plain static just slightly in the background. As I bring the signal generator output down the background noise gets louder but it never wipes out or overloads the receiver altogether as I can still hear the generator and the background noise and this is down to the same squelch threshold I get when on the dummy load. I am hesitant to call this desense as say when one of the duplexer cavities isn't tuned correctly. Then it is obvious because the transmitter totally wipes out the signal I am feeding it from the signal generator. I thought perhaps the preamp was the culprit so I took it out of line but sill experience the same issue. I am thinking that possibly the repeater output from the antenna is getting back into the repeater cabinet? I took a handheld scanner and set it on the same frequency as the receiver and connected directly to the rx port on the duplexer and can hear the noise there as well. I do hear a slight buzzing in the audio of the receiver almost like 60hz whenever I key the transmitter with the squelch wide open and no input signal present using the antenna. I don't hear it when using the dummy load though. I would like to think that the duplexer is tuned correctly or fairly close as there isn't any desense when terminated into a load. The last thing there is a single phase 7200 volt primary line servicing our neighborhood probably less than 100 feet from our house that I wonder is the culprit. I don't hear any arcing or power line noise with just the receiver squelch open but maybe when I transmit there is some mixing going on? Thank You Tom Elmore KA1NVZ Anchorage, Alaska
