Thanks Jim,
I'm wondering if I can take advantage of this to create a switched, 3 legged
antenna that will have the same gain/pattern as 2 switched broadside dipoles.
Looking at the diagram below, I'll switch from using wires 1 and 3 for a
northeast/southwest pattern to using 2 and 3 for a northwest/southeast
pattern. This would work nicely for me cuz there's a big cliff to the north
side of this setup so I can't get a support out that direction.... not to
mention less wires to hold up in the air. Does that make sense? Again, it all
depends on the vee enclosing a 90 degree angle being just as efficient as a
broadside dipole!
north
-------------------------------o o--------------------------------
1 | 2
|
|
| 3
|
|
Gary Slagel/N0SXX
Hot Springs, SD
http://marina.fortunecity.com/sanpedro/351
--- On Fri, 9/25/09, jimlux <jimlux@earthlink.net> wrote:
From: jimlux <jimlux@earthlink.net>
Subject: Re: [TowerTalk] modeling a v shaped dipole
To: "Gary Slagel" <gdslagel@yahoo.com>
Cc: "TowerTalk" <towertalk@contesting.com>
Date: Friday, September 25, 2009, 11:03 AM
Gary Slagel wrote:
> I didn't do a very good job of describing the antenna. I'm not really
> folding the ends back into a C. I'm making a flat V.... like an inverted
> Vee but with the ends horizontal rather then drooping to the ground.
>
> I didn't expect much effect as I brought them back to enclose a 135 degree
> Vee but I was surprised that when the Vee was enclosing only a 45 degree
> angle, EZNEC still showed it with an identical pattern to a broadside
> dipole. So... if the pictures I drew below are understandable, I wouldn't
> have thought these two dipoles would have an identical azimuthal pattern!
>
> ----------------o o---------------- broadside dipole viewed from above
>
> o o 45 degree vee dipole viewed from above
> / \
> / \
> / \
>
Oh yeah.. the pattern will be almost identical.. The "phase center" of
the bent dipole is about 1/4 to 1/3 of the way from apex to tails,
depending on the angle.
Think of the far field as being the sum of the fields from a bunch of
little chunks along the antenna. When you bend it, the direction of
current is slightly different, but since it's matched on the other side,
the "off center-ness" cancels. So now, all you've really got is the
same as if you had a sort of stepped dipole (with magic non radiating
interconects):
o o
- -
- -
- -
_______________________________________________
Gary Slagel/N0SXX
Hot Springs, SD
http://marina.fortunecity.com/sanpedro/351
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