TopBand: high angle versus low angle radiators

[w8ji.tom]

Hi Bill,

Please excuse my last post, I might have a good excuse for not being as
clear as I like. I just recovered from food poisoning, and after a week of
104-105 degree temperature I'm a little "fried".

I'm not disputing anyone's observables, but some presented as facts are
almost certainly due to other causes.

Let me expand on what Earl said a bit, in shorter form.

It was theorized wave angle can be too low from a horizontal, in my case it
was theorized 160 feet was high. It was also mentioned a Beverage might not
work because the wave angle is too low, and a horizontal antenna might not
work as well over "good" ground.

If that stuff comes from books we rely on, we should have a look at those
sources! They need edited or corrected. It is THAT stuff I refer to as
"weird science". The stuff in the cow pasture might be a better but less
politically correct name.

I modeled a simple inverted V at 130 feet. Here are the results:

poor soil .0005 S/M 90 deg 4.93 dBi, 30 deg 1.45 dBi, 15 deg -3.35 dBi

fair soil .015 S/M 90 deg 6.8 dBi, 30 deg 2.57 dBi, 15 deg -2.66 dBi

perfect ground     90 deg 7.58 dBi, 30 deg 2.96 dBi, 15 deg -2.43 dBi

This plainly shows better soil helps at all angles, low and high. The same
is true with a vertical. Bad grounds do not make good performance, unless
our goal is to heat the earth!

As for my antenna being too high at 160 feet, over medium soil the modeled
difference at a 90 degree transmission angle is about 0.7 dB compared to an
antenna at 70 feet . That is hardly a measurable difference when compared
to the 30 plus dB null of a vertical at 90 degrees transmission angle!

If the 90 degree wave angle were important, the vertical would be a useless
antenna and there would be little or no observable difference between a
dipole at 160 feet and one at 70 feet or less!

It's easy to see better ground conductivity, even to the extent of laying a
large screen on the ground, improves performance at ALL angles (including
low angles) for a low dipole.

This trend holds true whether the antenna is at 160 feet or 60 feet, poor
ground does NOT enhance a dipoles low angle performance, neither in theory
or in models. It did not enhance low angle performance in commercial
measurements either. And if that is in a textbook, it needs corrected.

There is also little or any difference between a dipole a 60 feet or 160
feet in gain at high angles.

Modeling a Beverage (something I don't have complete faith in because of
the distance from the wire to earth) also shows the Beverage is an
excellent high angle receiving antenna, even though as you point out is a
lower angle antenna than a conventional dipole at modest height.

Clearly I am not disputing anyones observables. What you observe is exactly
what I observe in the respect that some days, in particular days when the
band is hot, a horizontal antennas performance often or nearly always
improves at or after sunrise. 

The only thing I disagree with is thinking we can pin down the problem to
one root cause with nothing more than a guess about what is going on. Now
I'd be happy to top load my 260 foot tower to produce what should be a 45
degree TOA if anyone wants to do a series of AB tests again for a week or
two. That would give a clear idea just how a 45 degree angle compares to a
maybe 5-15 degree angle from the conventional antenna.

Polarity would not be an issue, just wave angle in a test between high
angle and low angle verticals.

73 Tom

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