For years I've used a center fed wire antenna fed with a balanced feed.
Some 2 or 3 years ago I decided to determine if the balanced antenna was
really balanced.
Nope, it wasn't. As a matter of fact it was unbalanced some 20%. So I took
the North end down to the south and the South end to the north leaving he
center feed point intact. Same thing except feeder current was now
unbalanced in the other leg. Humm, what's going on. I was using a pair of
lab grade very carefully calibrated RF amp meters to measure current in the
feeders. Took these to the top of the tower, inserted them in the feed
point and discovered that the antenna was indeed, unbalanced. It wasn't
feed line unbalance. Good, because I took a lot of care in installing the
feedline. In looking at the terrain, location of trees to which each leg
passed, the house and a few other things, all of which was some distance
away, I concluded that the soil conductivity under the antenna was not the
same thus giving me a unbalance. Hard to imagine. Measured the wire
lengths again only to find that they were with in 0.5" of being equal. Not
bad for a total of 256 ft of #12 hard drawn copper swinging in the air.
One day last Fall while mowing the grass it dawned on me. The field for the
septic system goes out to the south yard. The grass is always greener and
grows more than on the other end as that end stays a good bit more moist
than the north end. Latter in the Fall and after a couple of days of steady
rain, the feeds were balanced only to observe some 3 days latter they were
unbalanced again.
What did I do to solve the problem? Move the antenna to a east/west
configuration. Problem solved. Now, under most all weather conditions the
feed current balance is better than 5%. In neither case did I have RF in
the shack where the Omni VI+ resides. I'm happy knowing that my antenna is
balanced.
73
Bob K4TAX
----- Original Message -----
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
To: "Carter Grabarczyk" <k8vt@ameritech.net>
Cc: "robert k stephens" <bstephens1@mindspring.com>; "Joe Word"
<joe_word@yahoo.com>; <tentec@contesting.com>
Sent: Tuesday, April 02, 2002 3:31 PM
Subject: Re: [TenTec] Orion RF hardening (was Is Jupiter better...)
> Point well made, and I agree.
>
> Just an aside, twisting parallel line exposes both conductors equally to
> outside influences and will improve the current balance. Surprising that
> you had so much trouble from a center fed. But, then I heard from someone
> who had an end fed Zepp without any RF in the shack, so go figure that, as
> it HAS to have 10 per cent or more imbalance by its construction.
> 73,
> Stuart K5KVH
>
>
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