Hi Guy,
If this gets too long, be sure to read the closing part. This was NOT
the first published independent test of tribanders.
Send reply to: "Guy Olinger, K2AV" <k2av@qsl.net>
From: "Guy Olinger, K2AV" <k2av@qsl.net>
To: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Antenna Measurements & the
Mosley ad.
Date sent: Mon, 21 Jun 1999 23:56:50 -0400
Organization: PVRC-NC
Long post snipped:
I must not have made my points clearly.
Point 1
You still seem to think I intended to say the polarization tilt was
due to the antenna being tilted. I tried especially hard to not give
that impression, even to the point of trying to directly say that is
was due to re-radiation several times.
While I NEVER said the cause was improper mounting, I might
have made it clearer. I hope this does the trick.
The most likely causes are nearfield re-radiation, far-field re-
radiation, and feed systems. Two out of three of the above are
different for every antenna measured.
Point 2
We ignore the absolute fact test equipment used, and HOW it was
used, implies more than a few dB of tolerance in the numbers
measured.
It is virtually impossible to measure gain to 0.1 dB, let alone 1 dB,
outside of a lab environment with freshly calibrated standards. I'd
wager the tolerance in the equipment and methods used easily
exceeded 2-3 dB. Take those measurements and the equipment
outside in an uncontrolled range, and anything can happen.
Especially when measuring in a null. Now this doesn't mean the
results are that bad, just that we have no idea if they are or are not
that bad...especially since they are totally unverified with any
attempt at cross checking with another method.
Point 3
I obviously wasn't clear enough in describing why the antennas are
all different. They have different patterns, they were tested in an
uncontrolled environment days or weeks or months apart, they all
have VERY different near-field patterns and even a difference in far-
field patterns.
As a matter of fact, the reference antenna was a dipole. It's pattern
was totally dissimilar to the other antennas, rendering it useless in
an uncontrolled near-field or far-field environment when the
measurement is made in a pattern null caused by polarity. It is the
scattering and tilt that FILLS IN the null and makes the antennas
all not have zero signal, along with the imperfect earth. If the
patterns are different, we can be absolutely sure the scattering
effects are different.
I certainly agree, when all that is ignored the test is a perfect
comparison with no room for error.
The best article I ever read on testing was one about pathological
science, and how a series of measurements were used to confirm
a certain theory. Turned out the results were given latitude because
of delta in the test equipment, and trying to measure differences
smaller than the resolution of the setup.
Each person making the tests had the same results as they
repeated the tests over and over, yet the results disagreed with
each other when the people were changed.
None of this is all that sinister, and it certainly doesn't imply
dishonesty. This is all just part of human nature, like the tendency
to dismiss whatever argues with what we believe to be true.
It would be nice, before one source is accepted as conclusive, if
some attempt at a cross check was made.
For example, did you all know that this is NOT the first time
Mosley antennas were measured by an outside tester and
compared to other antennas in a similar test?
ARP, a journal that was an independent technical report (appearing
in volume II No. 3 ), did a similar test but used distances of 105
meters, 3000 meters, and 10,520 kilometers distant. They used a
more accurate field strength indicator than Ward and Steve, and a
different test protocol that STILL A-B'ed the antennas.
The gain rankings for 10-15 - and 20 were:
KLM KT34XA 10.9-10.3-9.8
TH-7DX 10.7-10.1-9.7
TB6EM (telrex) 10.3-9.8-9.6
**TA-36** 10.0-9.4-9.1
TH-5 9.3- 9.0- 8.9
*CL-33* Mosley 9.6-9.0-8.5
Before everyone leaps with both feet of top of Mosley, and ruins
their business with techno-nonsense about how pure and accurate
the triband tests are, we have to answer the question why a similar
test a few years earlier reached what seems like different
conclusions.
My suggestion is that these cluttered range tests are mostly
useless when the differences measured are that small, as theory
and good measurement protocol predicts they should be.
I don't expect those with preconceived notions or a mind-set about
the gain of Mosley antennas to accept that data, but it is every bit
as valid as the data in the recent study. Neither has any reliable
validation, neither was perfect.
It would be a shame if we ruined the business of someone who
made an antenna that was actually within a few dB of every other
antenna, with the damning evidence based on one report that used
less than ideal equipment and methods. In fairness, this
disagreement with another independent test using similar protocol
should be mentioned.
73, Tom W8JI
w8ji@contesting.com
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