[TowerTalk] Other triband tests disagree

[Tom Rauch]

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

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm