[TowerTalk] Flat top vs Inv Vee

[w8ji.tom]

Hi Bill,

The first line I wrote in my earlier reply was:

"Folding the legs down mainly changes efficiency by decreasing feedpoint
impedance and lowering the effective height of the antenna."

I think that says it correctly.

> >Model it, and you will see the VERY small difference between an inverted
V
> >DIPOLE and a regular dipole. 
> 
> I don't care what your computer says.  A flat top dipole will outperform
an
> inverted vee dipole at the same feedpoint height EVERY time.   By more
than
> a small amount.  This is my experience, and many others that I have
talked
> to over the years.  

I appreciate the input Bill, we all have feelings or opinions of which
antenna we think is better. That's what makes antennas fun to discuss and
build, and maybe we learn something along the way. 

I don't worry much about "Veeing" the legs a bit. I just mount the antenna
a few feet higher. For example, an 80 meter inverted V dipole at 180 feet
provides almost exactly the same performance as a perfectly flat dipole at
160 feet. It's much easier for me to have a single 180 foot support than
two 160 foot supports, especially when I want to build a phased dipole
array. I do try to keep the legs pulled out but I never worry much unless
they are less than "maybe" 100 degree angles.

I think the folklore surrounding the "inverted Vee" dipole antenna stems
from forming a "mental picture" that radiation is "canceled and eliminated"
by folding the legs in. It's very important and very useful in all antennas
to remember that opposing fields (such as those caused by folding the legs
together) cause the antenna to have a lower loop radiation resistance, and
it is only the reduction in loop radiation resistance (and the increase in
current that accompanies it) that increases losses.

Yagi's work that way, loop antennas do, and so do shortened verticals or
dipoles. The "inverted Vee" dipole follows the very same rules, no matter
what rumor might dictate.

Unless the dipole is "Vee'd" at an angle sharper than 90 degrees, there are
no noteworthy changes other than a slight lowering of radiation resistance
(slightly increasing the already insignificant I^2R losses of the dipole)
and a lowering of the effective height of the antenna. Nothing vanishes,
except the requirements of an additional tall support.

73 Tom

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