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[TowerTalk] Triband tests

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Subject: [TowerTalk] Triband tests
From: (Tom Rauch)
Date: Thu, 24 Jun 1999 13:35:41 -0400
Hi Dave,

> While I have not been involved much with the testing myself, I'm aware of
> the procedures, results, etc.  Our testing methods are not all that
> different than those used by K7LXC and company although we do  "A/B" test
> antennas.  Steve's methods, while not necessarily yielding totally
> accurate numbers in an absolute sense, should  yield reasonably accurate
> numbers in a comparative sense.  I would guess easily within a db.
> In the land mobile world, our only concern with antenna performance is
> radiation focused on the horizon.  Obviously, the more the better since
> our only mode of propagation is ground wave..  This validates our goal of
> maximum radiation on the horizon.  It also validates us using two antennas
> at reasonable heights above ground level (at least high enough to have
> fresnel clearance).

Then your test is a good one. 

First, the antennas are vertically polarized and at VHF and so don't 
face the same problems as measuring an antenna where a shift in 
polarity could produce extreme changes in signal level.

Second, you are measuring the antennas at an angle where you 
intend to use them.

> Our situation in the HF world is completely different.  If you have two
> stations (a few thousand feet or a mile apart) with antennas at reasonable
> distances off the ground (say 50 or 100'), it would seem to me that you're
> measuring the ground wave capability of the antenna (which does little or
> nothing toward working most DX).  I'm not sure how one would go about
> measuring the gain of a given HF antenna at reasonable launch angles (say
> 10 to 40 degrees). . . but the methods used as I understand them, aren't
> going to evaluate this aspect of performance.

That's correct. 

Another thing everyone ignores is the equipment used adds error. 
No result is perfect, especially when the equipment is not lab-grade 
equipment. A Bird meter alone will add almost one dB of delta 
when used in this manner. That alone, with the slightest additional 
error (such as reading a display from another angle) could cause a 
1.9 dB gain antenna to be over 3 dB, and a six dB gain to move 

Everyone should understand the results are never absolute to the 
point where they can be expressed to a fraction of a dB. 
> Who cares what the ground wave gain performance is?   Am I missing
> something here???  Perhaps so (I don't claim to be an antenna design
> engineer).

It may have been a good comparison Dave, it might not. Any test of 
horizontal antennas certainly would have been much more accurate 
if done at 500 feet or even less distance in a clear area rather than 
over a long path where attenuation of the actual signal is so severe.

73, Tom W8JI

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