Intermittant Duplexer ?

[arlojanis]

There have complaints for a while about noise on received signals on a VHF repeater. Everytime I checked the duplexer and repeater on duplex on R2600, there was no desense. This week I checked duplex operation again and receive sens was 1 microvolt and a lot of desense noise. I replaced the duplexer and now repeat is OK. I checked original duplexer the next day on another repeater on same frequency and there was no desense. The duplexer is a Wacom WP-641 BpBr later black model. 1300 kHz spacing. I have seen duplexers change a little with temperature or vibration, but this one is not affected by them. Have you ever seem a duplexer behave this way?

[Wowbagger]

I've seen those symptoms, but the problem wasn't the duplexer - it was the feed line was ceasing to be.

Everything looked good terminating the duplexer into a load, but on the air it went to crap. If you can, sweep the feedline and see if it looks OK.

(in my case that didn't help: a break 700 feet up on a 75 ohm feed line feed via a quarter wave transformer is kinda hard to see on a 50 ohm spec-an.)

[AEC]

I agree with wowbagger...

Bad feedlines always introduce noise and allows ingress of IM products, even the self-generated type.

RF coming back into the cans via the TX or even mixing caused by nearby transmitters can begin the process.

Improperly 'sealed' RF is a gremlin for duplexed systems.

[Bill_G]

+3 on the cables and connectors. The tug and wiggle test on the phased cables is a good idea when checking a duplexer. Sometimes the older ones used silver and/or copper that tarnished over time requiring cleaning. Every so often you find one that has a vane with cracked solder or a bad reject tuning cap. Most of the time it is the feedline and antenna that have gone bad causing the intermittent noise.

[Jim202]

There have complaints for a while about noise on received signals on a VHF repeater. Everytime I checked the duplexer and repeater on duplex on R2600, there was no desense. This week I checked duplex operation again and receive sens was 1 microvolt and a lot of desense noise. I replaced the duplexer and now repeat is OK. I checked original duplexer the next day on another repeater on same frequency and there was no desense. The duplexer is a Wacom WP-641 BpBr later black model. 1300 kHz spacing. I have seen duplexers change a little with temperature or vibration, but this one is not affected by them. Have you ever seem a duplexer behave this way?

You will spend a pile of time trying to locate the source of your problem noise. It is best to almost shot gun the issue. I would start with the feedline and take a close look at it. You didn't say what the coax cable your using going up the tower.

Take a screwdriver handle and start tapping on all the connections inside the building. Be gentle, as it won't take much to make the problem go away, but it won't come back for a while when your trying to locate it.

I have spent as long as a year going after this type of problem. Just make sure you keep track of what and where you have spent time looking for it.

Another point to ponder is does the weather have anything in common with the problem?

Does it happen more when it is dry or wet out?

Does this happen more when it is windy outside?

Is there any rusted hardware on the tower?

Is there any loose hardware or antennas on the tower?

Are any of the coax cables moving around in the wind on the tower?

Much of the above will require a trip all the way up the tower to the top. Make sure who ever does the climb, takes their time and looks at everything on the way up and down. I have missed items myself on the climb up and caught them on the way down. Go slow and tug, push, pull on every item along the way.

Check the grounds on equipment in the radio shack. I have seen loose grounds even cause all sorts of issues. Don't forget the surge protectors on the coax cables.

Jim