[AReU] Basic Antenna Repair

[Bob Haynes]

I would like to share an experience with the members of our group who may be looking for very basic repair techniques. 
Nothing magic or very sophisticated  was done - just the most simple of techniques were used.

A few years ago one of my friends gave me a two meter antenna.
I found out why recently when I put it way up in the air and could not bring up the Brandon Repeater with 50 watts.

It is one of those antennae with a thick loading coil rod 18" long, topped by a whip, giving the driven element an overall length of 50 inches.
The driven element is mounted on a metal plate at the bottom, and there are three radials each 20 inches long sloping down at 45 degree angles.
The antenna LOOKED like it was in excellent shape.
I thought of bringing it to the AReU meeting so the fellas could help me get it working, I knew that first I needed to run some simple tests to see if I could figure out why it was such a lousy antenna.  

So I dragged out my Fluke meter and took a few ohm readings to test for continuity and shorts.
There was good news and bad news.
The good news was that the center conductor of the SO239 was conducting to the driven element
The bad news was that the center conductor was also conducting to the base plate and the three radials.
Interestingly enough, the outer conductor of the SO239 was not connected to anything.

So I got out my wrenches and took the driven element off.
My driven element was screwed onto a metal barrel which goes through (and was touching) the base plate.
Since the driven element was not insulated from the base plate, I had to find out why, so I kept taking the driven portion apart.
There was a plastic washer under the plate where the driven element screwed on, but nothing to keep the threaded portion from touching the edge of the mounting hole through base plate.
I realized the washer needed a raised portion to provide the proper insulation, and as I was examining the washer, I turned it over and realized the problem.
The washer was installed upside down.  The raised portion had been facing away from the base plate.
So that took care of part of my shorting problem.
I noted that the metal bottom of loading coil also touched the base plate when it was tightened down, so I dug into my collection of salvaged washers and found a rubber one just the right size to place under the coil  
So I reassembled the antenna and ran tests with my ohmmeter.
The center conductor had continuity to the driven element, and it was no longer shorted to the base plate.
But I was baffled as to the reason the outer conductor of the SO239, which was not connected to anything.
I believe part of this antenna is missing.  
At first I thought I could solder a ground wire to the edge of the SO239, but I chickened out in fear of melting its plastic insulation.
I considered pinching a flat metal piece under the upper edge of the outer conductor of the SO239, but this surface is extremely narrow, and I had no idea how I could avoid shorting the outer conductor to the inner conductor by doing this.
So I looked through my junk box and found an old car battery trickle charger I have not used for 20 years, and have no intention of ever using it again, now that I know the value of regulated and floating chargers.
I noticed the battery clamp with interest.
Then I grabbed a piece of coax and screwed the PL259 into the SO259 of the antenna.
I tried the battery clamp on the smaller portion of the PL259, and it was a good, tight fit.
So I unscrewed the nut holding on one of the radials onto the base plate and found a ring terminal that was a good fit.
I soldered the ring terminal onto one end of some stranded wire.
I reinstalled the radial and left the grounding wire in place.  
I left the battery clamp in place on the PL259 so I could use the shortest length of wire to make that ground connection.
I cut the wire to length and soldered it to the battery clamp.
Then I re-tested the antenna with the ohmmeter:
I still had center to center continuity,
No short of center to ground,
and now I had continuity of the coax shield to the base plate and radials.
I then placed my antenna on a post in my back and ran an SWR test and got a very good reading.

Sure feels good when I win.

73,
Bob WB4AKA
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