TopBand: Another great Beverage idea

Mon, 23 Jun 1997 15:08:30 +0000

> From:          Eric Gustafson <n7cl@sparx.mmsi.com>

> >http://www.anarc.org/naswa/issues/0497/tech0497.html
> 
> I read this page.  It is indeed humorous.  But it contains a major fallacy
> that should get pointed out.

I haven't read the page, but someone mention a web page 
somewhere had a funny description of how to guesstimate 
termination impedance.

On rec.radio,amateur.antenna someone mention mentioned a web page 
somewhere described measuring termination impedance at the 
feedpoint, with some type of fixed termination on the far end or with 
the far end open. While termination resistance can be measured at the 
feedpoint, the method relayed to the newsgroup was very wrong.

One proper way to measure the proper termination value is to SWEEP 
the antenna over a reasonable frequency range, so you cross points 
where the wire is even and odd quarter wavelength multiples long.
The far end termination is adjusted until the impedance (SWR if 
that's all you can measure) at the feedpoint is as UNIFORM as 
possible as frequency is varied.

Another way is to measure current all along the line, and adjust 
termination for uniform taper as the current measuring device is slid 
along the entire antenna.

I have thought about trying to use the geometric mean of the high 
and low impedance values measured also, I think that would work. But 
"guessing" at a termination and concluding termination is properly 
set to the value measured at the feedpoint without a frequency 
sweep is worthless.

>In the article, it is stated that improving
> the ground conductivity benefits the operation of the beverage antenna.
> Specifically, antenna effeciency improvement is mentioned.  While it may be
> true that the antenna effeciency may be raised, it is _NOT_ true that this
> improves the operational characteristics of a beverage antenna.  The
> beverage is a traveling wave antenna which _depends_ on close proximity to
> a poor ground for its proper operation.  If you doubt this, erect a
> beverage over salt water or a wire grid ground mat and see how well it
> works.

Like you suggest, I've never found a ground so good that the 
Beverage quit working. I don't think anyone will.

Remember a very bad effect occurs in the Beverage. It is so close 
to ground the current tapers greatly along its length. I measured 6 
dB loss per 500 feet over soil of 15mS/m. A counterpoise 
reduces that loss, and so it might improve performance (just a 
guess) if the current taper is reduced more than the disadvantage of 
reduced e-field tilt. 

> OK.  So I'll admit that the irrigation was unlikely to improve the ground
> conditions enough to kill the beverage performance.  It is the erroneous
> concept that I object to.

Now consider this, the current taper is 6 dB per 500 ft in antennas I 
have measured. How much good does it do to extend a properly 
terminated antenna beyond 500 ft IF transmission loss through the 
antenna is 6 dB per 500 feet? How clean would the pattern be 
(necessary for high F/B ratios) even if the antenna was perfectly 
terminated??

> If you have very good ground, a (properly configured) EWE is the antenna to
> use.  If you have what most of us have for local ground conditions, then
> the beverage is very appropriate.

Because the end wires act like verticals with equal current and 
proper phasing, and the good ground prevents the horizontal wire from 
messing up the system. It is a VERY ground dependent antenna, that 
should work best over a large wire mesh ground.

EWE's don't work at all over my 4 mS/m soil here near Atlanta. 
73, Tom W8JI 

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