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It is best to tune an antenna for the particular part of the band you intend using the most but, as it was, tuning a quarter wave whip for the centre of the band was good enough. All I want to use it for is a couple of local FM repeaters so nothing special is required. The first radio I used was a 2m handheld with one of those rubber things and a quick quarter wave was a lot better than that.

The antenna attaches via a short piece of 6mm copper tubing with an M5 thread down the centre. Taping the thread forced the lower part of the tubing to be just a little bigger than 6mm and formed quite a good thread inside the tubing. If I hit a tree, the soft copper antenna breaks off and I make another one for 50 cents. So far I have hit some fairly low trees quite fast and it has stood the test. The antenna itself is made of a piece of 3mm hard silver solder. It conducts well and is quite strong in the wind but bends enough when going under low trees.

I made the base from a small round piece of single sided circuit board. Instead of etching it I simply ground the unwanted copper away using a bench grinder. Its like working on a fine watch with a sledge hammer and pick axe but, if you are careful enough, it works fine.

Cross section diagram


By measuring the resonant length from the open part of the RG58CU, the SWR was low enough to leave alone. When I tested it with the SWR meter, the needle didn't move on REFlected power but threw the needle against the top for forward.

To protect the whole thing from water I used some hot melt glue and gooped up the entire thing. On colder wet days, the hot melt glue does its job and keeps the base metal clean and free from corrosion. In summer, when its hot, the glue becomes a little softer and sometimes runs a little but this is good. It resticks the stuff. In any case, it isn't too hard to gunk it up again.

Finished antenna

Of course, to use the same thing for 70cm, or any other frequency over 2m, all I have to do is screw on another piece of tubing. In fact, all that needs to be done for 435MHz is to leave the antenna in place. The pattern is a bit toppy but will transmit OK if properly tuned for 145. (¼ wave for one, ¾ wave for the other ie. 145 x 3 = 435)

Bottom of antenna with thread.Bottom of antenna with thread.

On the top I added a short length of 2.5mm copper wire for tuning. The silver solder is far to hard to cut with a set of normal electronic style clippers. After calculating the length, I made the solder about 30mm short before adding the copper. This was done by grinding both the solder and copper at an acute angle to allow a reasonable joining surface so soft solder could be used there as well. I have hit the antenna on low trees and inside carparks and the worst damage was a slightly bent piece of copper. Even if it broke off, it is short enough not to affect the SWR too much.

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