Quote:
Originally Posted by Eric
Have any of you tried using a tower as a J pole antenna for 20 or 40
meters?
According to calculations, it looks like a 50-foot tower would be about
right for 14.1 MHz with a 16.6-foot matching section that could be made
out of aluminum tubing and spaced out about 1.5 feet.
This should make a decent low-angle radiator without needing any buried
ground wires (which would be difficult to put in around here).
Then I thought maybe a taller tower, perhaps 80 feet, with a triband beam
on top, could perhaps be made into a J-pole for 40 meters with the beam
acting as a hat.
Obviously I haven't thought this through very much but I was just
wondering if any of you had tried any of this or knew of any articles or
websites that describe such a project.
|
I turned my 65 foot rohn 25 into multiple antennas. #1 160 meter shunt fed, #2 80 meter shunt fed, #3 160 meter inverted L. #4 20 meter J-pole, soon to be fixed up with a 10 meter version. The 20 meter J seems do do quite well on the whole band, and the autotuner on the Kenwood 2000 will tune it from roughly 13.2mhz, to somewhere in the 15.5 mhz. SWR is flat "as a fritter" in the targeted middle of the band. At 100 watts iv'e worked Russia and Japan, and the occasional asiatic islands on Psk 31. USA local is a breeze. I simply measured the tower the appropriate distance (3/4 wave) and bolted the 1/4 wave section to the tower, approx one foot out. But be carefull of the top of the 1/4 wave swinging in the wind, it will de-tune the antenna in a hurry. Also, I have all my guys insulated from the tower.I have also thought about loading a 40 meter 1/4 wave at the very bottom , and using a "top hat" as well, to get that needed 100 foot or so for a match on 40. I shunt fed the tower once for 40 , but had a cruddy ground plane at the time, results were quirky. New attempt is coming in a few days...good luck...Dave KC5UTA