[TowerTalk] modeling a v shaped dipole
gdslagel at yahoo.com
Fri Sep 25 09:19:37 PDT 2009
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
From: jimlux <jimlux at earthlink.net>
Subject: Re: [TowerTalk] modeling a v shaped dipole
To: "Gary Slagel" <gdslagel at yahoo.com>
Cc: "TowerTalk" <towertalk at contesting.com>
Date: Friday, September 25, 2009, 7:27 AM
Gary Slagel wrote:
> Hi guys,
> I tried to model a v shaped dipole yesterday and was surprised by the
> results. I'm looking at a dipole with the ends bent back toward each
> other rather then an inverted vee. I started with a straight dipole,
> then bent the ends toward each other so they enclosed a 135 degree
> angle, then bent them to enclose a 90 degree angle, and last a 45
> degree angle.
> The azimuth pattern I got was identical for each configuration. The
> direction was different depending on how I rotated the wire to change
> the angle, but the pattern was identical.
> Does this seem reasonable or was I making an error or does eznec have
> a problem modeling this? I was using the free eznec provided with
> the arrl antenna book.
the entire antenna is all in a flat plane? so it's looking sort of like a big "C"
Most of the pattern is determined by the middle of the dipole, so bending the ends doesn't do much other than change the feedpoint impedance. a half length (1/4 wavelength long overall) dipole with capacity hats to make it resonant has almost exactly the same pattern as a full sized dipole.
In fact, an idealized dipole has about 2.2 dBi gain, while an infintesimally small dipole (called a Hertzian dipole) has a gain of about 1.7 dBi.. unless you plot the two patterns on top of each other, you wouldn't notice the difference.
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