On 24 Sep 2002 at 13:14, W7CW Jay Ostrem wrote:
> I was just curious if anyone has toyed with the following idea. It seems
> too easy, so it probably won't work, but looks promising on EZNEC.
>
> It appears that the fewer elevated radials you use, the higher they must be
> to avoid losses.
>
> I have a 130ft tower. I was considering running two radials off the top of
> the tower in opposite directions, limiting the droop to about 30 degrees per
> side.
>
> The vertical part of the ground plane comes off the top of the tower out
> and away at a slight angle for about 50 ft of its length, and the rest comes
> straight down. The tower will be detuned with a drop wire and capacitor.
>
> Any thoughts or experiences?
>
> 73 Jay W7CW in Wyoming
>
Hi, Jay-
This sounds like a variant of the 30-30, popular on 40 meters
in the early part of the 20th century. They ran a wire 30 feet
vertically and then another 30 feet horizontally, and fed it
against ground via a parallel-resonant tuned circuit
(voltage feed). You are simply moving the feed aloft to the
current point and direct feeding with coax. Should work.
Stand by for the usual barrage about the need for radial
grounds on the ground beneath it. You are describing the
most simple variant of the- er, uh- dare I say it? The
Bobtail/Half Square family. :o) It would work best if the
'horizontal' wire were truly horizontal, but should still give a
fairly good account of itself on top band. Add another equal
length horizontal wire going in a 180 degree opposite
direction, tie it all together and feed from the ground against
a small counterpoise with a resonant tank, and you have a
full wave "T" antenna. Or break it aloft and direct-feed
with coax and it will probably also work well. You might
give all the naysayers a polite hearing and then go ahead
and try it anyway. :o) You can report back to us with
your results. If it makes you feel better, go ahead and put
a large radial field on the ground beneath it- but a small
counterpoise will suffice should you decide to voltage feed it
on the ground. :o) Or just leave out the on ground radials
entirely and feed it aloft with coax.
73, David K3KY
P.S. Just to clarify, I should have said "half wave T". A quarter
wave T requires an extensive on-ground radial field to
work well, and is current fed at ground level. A half wave T
has the current point aloft and can be voltage-fed at ground
level against a small counterpoise. Chop off one of the
horizontal wires and it should still work about as good.
http://www.angelfire.com/md/k3ky/page38.html
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