Celwave 5085-3 duplexer instablility

[mancow]

We have a small Vertex VX7000 repeater at work that was in a tac van but it going to now be used as a stationary repeater. It has a Cellwave 5085-3 duplexer mounted to the top that was factory tuned to 155.055 TX and 158.880 RX. Our new freqs are 159.420 TX and 154.010 RX. So, I put it on the analyzer tonight and began the process of tuning it. I swapped sides to keep the tuning as close to the factory as possible. Everything seemed fine at first but I am running into a stability issue. When I got to torque down the lock nuts the notch goes from a nice deep V to a wide valley. If I apply lateral pressure to the tuning rod the deep notch returns. I can get everying tuned up but again, when I go to lock them down it seems to lose its notch tuning and goes somewhat flat.

Has anyone encountered this? Could it be the years of hot and cold and moble use that fractured or otherwise damaged something inside? It's as if the lock nut is causing the metal to slightly warp and cause an open circuit somehow. I tested it prior to messing with the tuning at the original frequencies and it looked fine but once those lock nuts were broke loose it seemed to cause issues.

Should I try to open the thing and see if there is something broken? If so, what would I look for? Has anyone else encountered this?

Thanks for any info or advice.

[Bill_G]

Those notch type duplexers with the locking nuts can be a bear sometimes. Tighten the nuts so you can still adjust the slugs. Keep a wrench on them if you have to because they love to move when you adjust counter clockwise. And then leave it alone. PITA but they work if you don't have a better duplexer. Just remember - if you're using one of these at a fixed location with other transmitters on site, this duplexer will do little or nothing to keep them out of your receiver.

[mancow]

I couldn't imagine this was normal but it sound as if it is. There are some rail transmitters about two or three blocks away. Hopefully they won't caus us issues. I had forgotten about them until you mentioned it. Thanks for the info. I will try to get the thing dialed in and will test it out at the site to see if we get hammered by the rr guys

Those notch type duplexers with the locking nuts can be a bear sometimes. Tighten the nuts so you can still adjust the slugs. Keep a wrench on them if you have to because they love to move when you adjust counter clockwise. And then leave it alone. PITA but they work if you don't have a better duplexer. Just remember - if you're using one of these at a fixed location with other transmitters on site, this duplexer will do little or nothing to keep them out of your receiver.