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[TowerTalk] Triband tests

To: <>
Subject: [TowerTalk] Triband tests
From: (Iowaguy)
Date: Thu, 24 Jun 1999 21:18:50 -0500

You have some very good points (as usual).

I certainly wasn't meaning to advocate vertical polarization for HF yagi
test!  I'm
still not sure how one goes about measuring relative (much less absolute)
gain at realistic launch angles (which is where the rubber meets the road).
Looks to me like all the methods described thus far are measuring gain at
the horizon, which
I'm not sure is very meaningful or relevant even in a relative sense (much
less in an
absolute sense).  What do gain measurements at a distant horizon really tell
us?  Perhaps more than I realize. . . it's just not obvious to me at this

In any case, I have enjoyed the thoughtful and civil dialogue on this
subject. . . which is of significant to all of us.

73 to all. . . Dave
-----Original Message-----
From: Tom Rauch <>
To: Towertalk <>; Iowaguy <>
To: <>
Date: Thursday, June 24, 1999 12:41 PM
Subject: Re: [TowerTalk] Triband tests

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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