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[TowerTalk] Antenna Measurements & the Mosley ad.

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Subject: [TowerTalk] Antenna Measurements & the Mosley ad.
From: (Tom Rauch)
Date: Sun, 20 Jun 1999 11:29:51 -0400
I wrote:
> > What about a condition where an antenna does not have a perfectly
> > horizontal radiation pattern compared to another antenna, say from
> > feedline radiation or re-radiation from clutter in, near or around the
> > test site?
> >
> > A problem with accuracy could easily occur, since the horizontally
> > polarized component is greatly attenuated over the same distance
> > compared to any vertical component. The slightest amount of
> > pattern tilt could greatly affect path attenuation.

You replied: 
> That presumes that the actual horizontal null is as deep as the
> theoretical one. Here the ground clutter and irregularity, as long as it
> isn't moving, tends to IMPROVE the accuracy of the test, since it takes a
> LOT more off-angle radiation to skew the result. And it's not like it's
> hard to level out a tribander against the horizon. And the dipole
> measurement is common to all the tribander figures, and though it might
> affect absolute gain, would not figure in the comparison.

The argument you give supports the fact the range is flawed
 and subject to scattering problems, and physical TILT in the
 antenna was never mentioned as a cause. Re-radiation and scattering
 are the causes I mentioned.
> >That's why it is
> > imperative, in a test range, that the antennas NEVER be tested
> > where site attenuation is high and/or where re-radiation could
> > greatly affect results.

As I did above.

> > If you want to see an example where this occurred, there is a web-
> > site that proclaims by removing an antenna tuner and using a stub
> > match, several S units were gain in field strength. The test protocol
> > was a groundwave path over a few miles on 80 meters.
> Depending on how grievously mismatched the antenna was, the result may
> have true for DX as well. Most of his power could have been radiating in
> directions he didn't care about, at the moon, or heating the sod. Did his
> contest scores go up after he made the change?

Hunh? What do contest scores have to do with anything?
Changing from a tuner to a matching stub has a minimal effect
on pattern, if any effect. The reason it shows  up as a large change 
is he MEASURED the results on groundwave at a large distance 
when the main antenna radiation was far overhead. 

> No disagreement whatsoever on the merits and particulars of the above,
> regardless of where I think the power was really going. But does it
> substantially apply to a COMPARATIVE test of extremely similar antennas on
> a common test jig?

Absolutely it does. It illustrates ONE potential problem perfectly.
> > The true data above is a shining example of why a cluttered
> > groundwave path with high attenuation should never be used to
> > determine efficiency or gain.
> You mean ABSOLUTE efficiency or gain. They were COMPARING apples with
> apples on the same test jig.

No, I mean what I said. The triband test did NOT compare Apples 
and Apples, it compared Mcintosh Apples to Big Red Delicious 
apples to an Orange at a distance of a mile or more where one 
could hardly see which was which because a million other apples 
and oranges were hanging all around.
> > Testing a horizontally polarized antenna close to ground over a
> > large distance is always a bad idea, even in a controlled test range.
> Except, Tom, this is EXACTLY the case we all have, unless you are on a
> 1000 foot tower, talking to another ham on another 1000 foot tower (well,
> maybe on W4AN's mountain, but that doesn't count...). The intent is to
> test the antenna how we use it. I can live with that and agree to never
> mention the gain as an absolute figure.

Here we finally agree. If I lived at the house where the antenna was tested
and I wanted to talk to the guy at the other house where it was measured, 
I'd use a different antenna. 

73, Tom W8JI

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