Hi Peter --
1)
I agree that dipoles at low hight have less gain than the vertical.
That comports with what I said.
2)
I am not considering what a dipole does at 1 wavelength or even
at 1/2 wavelength - as that is not realistic or feasible for nearly
all hams on 160, 80, or 40 meters. This discussion is primarily
about a 160 meter Inverted L - which is kinda like a combo
vertical-horizontal antenna and there is no way we are going to
be able to hang a dipole at one wavelength height. Thus, I consider
that an inappropriate comparison or measuring stick in this case.
3)
I respectfully disagree with your claim take off angles are manifested
by the ionosphere.
When researching a big vertical for my back yard,
several Extras did modeling for me comparing the 45 foot vertical
with 80, 40, and 20 meter dipoles at various realistic heights
above average ground, using NEC, EZNEC, and HTFA modeling
programs. These all confirmed what I said, and is the basis for
what I said.
Moreover, I do not believe your statement is correct. I believe the
take off angle is not a function of the ionosphere... it is a function
of the antenna over the ground (i.e. terra firma or the dirt below.)
After the radio wave emanates or radiates from the antenna,
then it might interact with the upper atmosphere, but it has to
radiate first, and that is a function of antenna design, materials,
and relationship to objects, such as good Ol' Earth.
In all the cases studied and modeled, the vertical antenna had a
lower radiation pattern than a low hanging dipole (it is like fairly
impossible for me to get a 1/2 wave 40 meter dipole up 1/2 wave
over the ground, so we used different realistic values, such as
that dipole at 25 feet, 40 feet, and 60 feet, respectively. We
compared the take off angles and radiation patterns with the
angles and patterns for the 45 foot monopole vertical. We
modeled the same sort of setup for 160 meters, 80 meters,
40 meters, and 20 meters.
In all cases the dipole radiated at a slightly higher angle than
the vertical, which is why the vertical is a better choice,
sometimes, than the dipole for low band DXing.
On the higher bands, the patters seemed to reverse for all
dipoles. The upper bands on the vertical radiated at slightly
higher angles and with higher take off patterns than the dipoles
on those bands, favoring the dipoles for DX on those bands. \
It is very often said that such large monopoles tend to be "cloud
warmers" on the upper bands, and good DX performers on the
lower bands. This was born out by the modeling charts. It also
coincided with what I have been reading in the ARRL Antenna Book
when comparing the take off angles and radiation patterns of dipoles
and verticals.
Note: We did not discuss the performance of "theoretical" dipoles
hung at 1/2 wavelength heights... that is not realistic at my QTH.
But I really do not think the radiation patters are affected by the
ionosphere - it is way up there in near space, and the antenna
radiates down here on earth according to its design, materials,
and proximity to other objects. The radiation pattern is already
established and a moot point by the time the radio wave reaches
the ionosphere. How can the ionosphere shape the take off angle?
That's my take anyway... Happy trails -- interesting discussion.
============== Richards -K8JHR ================
Peter Voelpel wrote:
. Radiation angles are determined by the height of the
> reflecting layer of the ionosphere and skip distances and probably almost
> the same on high and low bands, if not higher on the latter while more hops
> are necessary.
> But, dipoles at low height and especially invertered V dipoles have much
> less gain at 10-12° then a vertical.
> A dipol at one wavelength will always beat the vertical with its additional
> ground gain except the vertical it is above salt water or the dipol is
> facing the wrong direction.
>
> 73
> Peter
>
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