This could also be one reason of the "36 Foot" myth It is said that best
results are obtained when the A99 or Imax is at 36' to the feed point.
Maybe it's not the relationship to ground as much as the length of the mast
acting as the counterpoise. If you want to go more than 36' then a ground
plane kit is recommended to lower the take off angle. Many have noticed good
results with the GPK above 36' but found it a waste below 36', HMMMM. I'm
only at 20' now on a push up with a tower coming in spring to get me to 36'
I don't want to go much taller A. because the wife would freak, and B. it
would become a lightning magnet in my one-horse-town.

Another thing to ponder is that the addition of the Balun may help the ERP
because you are eliminating one of the 2 counterpoises (mast and coax) which
would certainly have 2 different velocity factors. This could possibly act
as a phasor in certain instances and cause an omni antenna to be "not so
omni"

There is a possibility that my ERP may have gone up after the balun
installation. Although problems associated with feedline radiation in the
shack decreased, the audio problems with the stereo in there shack increased
slightly. Maybe there is a tad more coming out of the stick and not being
wasted elsewhere?

Once again just pondering, I may be WAY off

Chad


"Jay in the Mojave" wrote in message
...
Hello Chad:

Wow good point here you have made.

Yes I agree with you here, the mast would become the counter poise, if
currents are choked at the coax. This is why these none ground plane
antennas will still work when a coax Balun is placed right at the antennas
connector, a Great point made here.

In the 1980's I had a terrible time installing a Sigma 4 antenna. As the
mast was pushed up the SWR changed. So I figured some how the mast and
maybe the coax, was apart of the antenna, and dropped the mast down a foot
at a time to get a decent SWR. I wish I had a Balun then.

Placing the balun down the coax at a 1/4 wavelength might work well on a
fiberglass boat and such.

One of the things while adding such things and testing them, is to keep an
eye on the field strength of the antenna. If something is done and the
field strength increases or decreases you want to see this.

In some cases antenna ranges will monitor the antennas swr as compared to
its field strength.

Jay in the Mojave


Chad Wahls wrote:
"Jay in the Mojave" wrote in message
...

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.



As you may have guessed the antenna is an Imax 2000. Which mounts to the
mast via a metal base that is directly coupled to the mast/tower. This
being said wouldn't the mast become the counterpoise at this point if the
coax is not? (The outside of the PL259 is directly coupled to the
mounting provisions.)

The balun was made out of spare junk on the premise that I NEEDED a
reason to go out to the shop, drink some beer and relax. What a better
project, a free one I made it removable for obvious reasons and have
thought about Jay's points a couple times when they were brought up after
construction of said device. This spring I hope to have a new
(different) tower and at this time will play with moving the balun from
the feed point to right before the ground rod next to the house. This
will allow the coax to act as it should and hopefully keep my feedline
currents down, wadda ya think?