Hello Dr Death:

Ok good deal I saw the impressive photos that Chad had there.

One thing to consider is that those fiberglass none ground plane
antennas use the coax outer shield as the counter poise or other end of
the antenna, so current will be seen on the coax. And in some case you
will see SWR changes from different lengths of coax, because the coax is
actually radiating, acting like a antenna.

I have had customers add in a line coax Balun on these type of antennas.
The Balun uses a Toroid Core, with the coax would around it. But the
trick here is that the Toroid Core is placed at 1/4 wavelength or about
102 inches down from the antennas connector. This allows the coax to
radiate for a 1/4 wavelength, possibility allowing for a low take off
angle, then choking off the currents beyond the 1/4 wavelength. Or the
coil wound coax Balun can be tried.

My personal experience has been that the coax Baluns didn't have enough
choking impedance, allowing the antennas lowest SWR frequency to be much
lower that what it really was, because the coax was also radiating and
acting like part of the antenna. But this was on a beam antenna, and not
a fiberglass type antenna.

Suggest its worth a try, to add a choke Balun at a 1/4 wavelength below
the antennas connection.

Jay in the Mojave



DrDeath wrote:
"Jay in the Mojave" wrote in message
...

Hello DrDeath:

Why do you want a Balun, and on what type installation are you going to
use it????

Jay in the Mojave


DrDeath wrote:

I am trying to build a balun. I chose the one on this web site as I like
the design
http://www.hamuniverse.com/balun.html
It states that, and I quote
"The number of turns is not critical because the inductance depends more
on the length of the wire (coax) than on the number of turns, which will
vary depending on the diameter of the plastic pipe that is used."
But it does not give the formula. It just says 18 to 21 feet.
I plan to use 4 inch pvc and I want to cover as much of the upper 11
meters as I can. Am I better off at 18 or 21 feet?


I'm just messing around with a home made dipole. I want the balun to cut
down on the TVI.