wrote in message
...
On Sat, 16 Sep 2006 14:25:35 +0200, "J. Kragh"
wrote:

Togethere wih a fellow amateur I am trying to design an endfeed halfvawe
vertical antenna for 50 MHz.

snip

Look at a J-pole antenna. Its really a stub section feeding a halfwave
antenna.

The impedence transformation has to go from coax (60-75 ohms) to
a much higher and possibly reactive load in the range of
1500-3000j(+/-)0-100 depending on dimensions of the halfwave antenna
relative to the actual frequency.

Yes. I have built three copper-pipe j-poles for 6 M. The overall length is
about 13 feet (4 meters) long. I made them predominantly from 3/4-inch
copper water pipe, which comes in 10-foot lengths in the US. I used a
reducer and about three feet of 1/2-inch pipe for the top part of the long
section. All of the connections are standard water-pipe fittings and the
soldering is with a propane torch on sanded and fluxed surfaces. These
three are among about twenty j-poles I've made for VHF/UHF. They seem to be
indestructible.

I was able to match about 80 percent of the 6 meter band under 3:1. My best
SWR was about 1.2:1 with a short length of coax and nothing special at the
feed point. A choke consisting of four turns of the coax is recommended for
decoupling.

I am a j-pole lover. I intend to try a flagpole or two at HF, someday.