W4ZT Repeater
Union City, Georgia
146.625 mHz (-600) no tone required but transmits 100 Hz

Diamond F23 Antenna Failure

On Thursday, June 27, 2002, we experienced a storm here that knocked the repeater off the air. After some checks I found very high SWR on the feed line to the antenna. I patched the repeater over to the four side mounted dipoles below the repeater antenna as a temporary measure. The repeater operated in this crippled mode until July 21 when Patty - kg4ncp, Rick - KC4HYM and Henry - KM4O and I got together to find out exactly what the problem was and try to fix it. We decided to take the Christmas lights down at the same time.

We had been experiencing some intermittant unexplained noise and desensitization for some time and had thought we had a bad coax connector or something else which we would find once we could schedule a routine climb up the tower. There were even theories that the Christmas tree lights were causing this problem. This unexpected total failure pushed that schedule up and the problem we found explains most of what we had been experiencing.

These pictures document that process. Click on the small pictures to see a larger picture in another browser window... Tony

Rick - KC4HYM, Tony - WA4UPE and Henry - KM4O pose for the camera before sunrise on July 21st
Tony up the tower at the middle of the dipoles we used for the temporary fix
At the base of the repeater antenna
Patty caught this jet headed towards Tony
Rick on the roof helping with the lights
Henry supervises...
Tony gets ready to test the antenna and feed line with the MFJ SWR Analyzer.
The feed line was good. The Diamond F23 antenna was BAD.
Tony starts down. The lights and the antenna are all on the ground
On the ground we disassembled the Diamond F23 antenna. In the base, the center conductor of the coax connector is brought out the side and coupled to the top (right end) of the inductor shown here with a small disc ceramic capacitor. DO YOU SEE THE PROBLEM?
Now do you see the problem?
This cold solder joint (FROM THE DIAMOND FACTORY) was the problem!
This was a defect in workmanship from the factory.
A good hot soldering iron and some solder fixed this problem.
This is the very top of the inside of the antenna. It's brass rod. After all these years the darkening of the surface isn't surprising BUT this bright copper looking spot IS! Best I can figure is we had some electrical discharge THROUGH the fiberglass to the brass rod. There was NO evidence on the fiberglass - inside or out.
We buffed the brass rod end to end with ScotchBrite and replaced a few of the foam spacers before reassembling the antenna. We tested the antenna with the MFJ SWR analyzer and it tested good. I don't believe the discolored spot had anything to do with the failure.
Tony heads up the tower before 0700 on July 22nd. You can see the antenna with its feed line pigtail hanging off the right side of the climbing belt and the PVC pipe which was to be used for a mid-antenna support hanging from the left side of the belt.
Here I am placing the repaired F23 antenna into the mount.
I'm waving from the top of the tower while mounting the support for the middle of the antenna. We decided to add this support to keep the antenna from moving around so much in the wind.
I took this picture of Henry - KM4O, Patty - kg4ncp and Brandy the dog on the way down after the job was done.
This repair appears to have fixed the problem. Our noise is gone and everything appears to be normal.

Last update was November 20, 2006 5:03