[Towertalk] antennas near water

[John Petrich]

Bill and the rest,

    A lot can be said about antenna performance in a fresh water
environment.  It seems to me that the distinguishing impact of a fresh water
environment on antenna performance involves consideration of both the
conductivity and dielectric properties and the physical (macro) properties
in the far field reflection zone or first reflection zone and beyond.  A
narrow river in a steep valley is not a fresh water enviroment in this
context.  A large river, large lake, or a large swamp in a relatively flat
area are what I think you are describing in your question.

    A fresh water environment has modeled out for me, and is described in
the ARRL Antenna Handbook and in W7XC's original QST article, as equivalent
to a "very good" ground.  The result is that the Pseudo-Brewester angle is
about 6 degrees through the HF spectrum.  My modeling attempts suggest a
significant improvement in low angle radiation from a vertical antenna over
fresh water compared to a vertical over  "average" ground at all elevation
angles below 10 degrees.

    A fresh water environment CAN be physically flat, homogenous, and have a
low radio horizon at distances that correspond to the far field reflection
zone and beyond for our HF antennas.  This uniformity can contrast with the
relatively cluttered and irregular far field reflection zone and beyond that
characterize so many real world regular earth enviroments.  A smooth and
uniform far field reflection zone and low radio horizon could be expected to
aid beam forming and contribute to low angle propagation efficiency.

    The performance of horizontal antennas are relatively little effected by
the electrical characteristics of any ground in the far field reflection
zone.  Vertical antenna performance is significantly affected by these
properties.  Both are benefited by efficient beam forming and a low radio
horizon if DX is a priority.

    I'd say that a fresh water environment can contribute to the performance
of any antenna to the extent that the far field reflection zone is uniform
and the radio horizon low.  Vertical antennas get the additional benefits,
unique to vertical antennas,  that come from a "very good" ground.

Regards,

John Petrich, W7FU


----- Original Message -----
From: "FireBrick" <w9ol@billnjudy.com>
To: "TowerTalk List" <towertalk@contesting.com>
Sent: Friday, April 19, 2002 5:18 PM
Subject: [Towertalk] antennas near water


> I've seen many postings about the improvement having an antenna near the
> shoreline.
>
> Just wondering...would having a tower and antenna on the shoreline of a
> large river provide a similar improvement?
> In ME where I would love to move to, there are MANY large rivers emptying
> into the bays and harbors.
>
> Would any gain be dependent on the direction/route of the river?
>
> Just curious.
>
>
> ------------------------------------------------------------
> A hangover is the wrath of grapes.
> ------------------------------------------------------------
>
> Bill H. in Chicagoland
> w9ol@billnjudy.com
>
>
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