Ground Loss may be less important than the ionosphere's condition at the
time you use the antenna...
If the signal from the NVIS I run was any stronger I get sued by those
locals whose receivers caught fire...The NVIS I use is 18ft above the ground
on 40m and 35ft on 75m which is sand for at least 600ft.
If Jim is looking for high angle short skip on 75m I would expect his should
do fine... I never heard what his goals were for the antenna.
I have a reference dipole at 50ft for both 40m and 75m and it doesn't
perform nearly as good, close in, as the NVIS antennas!! What I have
learned is that the ionosphere has to cooperate. You have to know whether
current conditions support 90 degree take off angles. It isn't there all the
time for anyone to use. There are days when NVIS just is worthless and
during the low sun cycle there is very little support for NVIS but its
starting to pick-up. So, if you can have a reference antenna then you are
in the best position to make comparisons and search for those times when
NVIS at 1/8 wave above ground will smoke a dipole at 50ft from just a few
miles to several hundred miles out. That has been my subjective experience
of one.
GO FIGURE! YMMV
73'
dave
wa3gin
----- Original Message -----
From: "Rob Atkinson" <ranchorobbo@gmail.com>
To: <towertalk@contesting.com>
Sent: Sunday, February 06, 2011 3:48 PM
Subject: [TowerTalk] Non-Guyed Support for 80m Horizontal Loop at 35 feet
> Let me save you some time Jim since I have been there and done it.
> Horizontal loops on 80 m. stink if they're only 35 feet high. That's
> too low to ground; they're too lossy to ground coupling. If you
> can't get it high enough in terms of wavelength it won't work well
> unless you compare it to an antenna even worse like a G5RV. Loops
> have to be high, real high to overcome their exposure to ground from
> being one or move wavelengths long. At least 70 feet but even higher
> is better. Four supports that tall is expensive, especially if they
> are free standing. You are far better off spending your money on one
> or two supports (or whatever the minimum needed is--use a tree if you
> have it!) for a center fed dipole 1/2 wave on 80 m. that is at least
> 50 feet high. less ground coupling due to smaller antenna exposure
> and slightly higher and more isolated from earth surface.
>
> To paraphrase Cebik, basically small and high beats big and low. If
> you are interested in the NVIS effect, 50 to 70 feet high will still
> give you that but without the huge ground loss.
>
> 73
>
> Rob
> K5UJ
> _______________________________________________
>
>
>
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