It's not necessary to place a vertical antenna at waters edge to gain the low
angle efficiency advantages of an oceanfront site. There are two zones of
interest: the area immediately adjacent to the antenna which primarily affects
efficiency (very important for transmitting and very unimportant for top band
receiving) and the Fresnel Zone which is very important for the very low angles
that difficult to achieve at most land sites. Salt marshes (e.g., W1KM) are
practical for long term installation but antennas over ocean water are rarely
practical except on ships. The most practical ocean front permanent
transmitting antenna is a land based vertical over an extensive radial system
sited so that most of its Fresnel Zone is over salt water.
73
Frank
W3LPL
----- Original Message -----
From: Guy Olinger K2AV <k2av.guy@gmail.com>
To: Tom W8JI <w8ji@w8ji.com>
Cc: Mark Connelly <markwa1ion@aol.com>, TopBand List
<topband@contesting.com>
Sent: Tue, 19 Aug 2014 21:21:03 -0400 (EDT)
Subject: Re: Topband: Modeling the proverbial "vertical on a beach"
On Tue, Aug 19, 2014 at 11:24 AM, Tom W8JI <w8ji@w8ji.com> wrote:
> Why would it matter?
>
> The receiving antenna does not matter, provided it responds to the wave
> angle at the receive site. It doesn't matter if it is loop, a 10 foot
> vertical, or a 200 foot vertical so long as the antenna does not null the
> primary wave angle for the incoming signal. It does not matter if it is a
> large receiving array or a whip, provided each are not nulling the primary
> signal arrival.
Or giving advantage to one or the other incoming angle in effect setting
the primary signal arrival
Not using a small omni RX antenna for this experiment introduces some
serious calculation issues. E.g. if the RX setup has pattern and gain, we
first have to know what incoming angle and direction a signal is arriving
at and then divide the pattern out BEFORE any comparisons are made. So how
do we know that? VOACAP has that built in where you are supposed to
supply the RX pattern, which otherwise defaults to omni.
No pattern is required to eliminate direction and elevation arrival
adjustments to reported readings if the antenna is truly omni. If the RX
antenna is "omni" and low enough then any enhancements are due to the
propagation or environment or the TX station's antennas, which is what you
WANT to see.
FURTHER, since nearly all ham TX antennas are NOT at water's edge, then any
tests looking for water's edge enhancement must do so by placing RX at
water's edge and placing another identical RX/antenna back on the beach a
few hundred feet off and another identical RX/antenna at typical shore site
antenna-distance-from-actual-water's edge as in 1500 feet for W2GD and
K3ZM.
Putting up and maintaining TX antennas right at water's edge and feedline
back to safe location for transceivers, etc, is something that likely
unworkable or will not be tolerated by those controlling public beach
fronts, would be a maintenance nightmare to begin with. These include such
things as guy anchors under water on the beach, that will not come loose
under typical random sand rearrangement underwater. Or continuous
corrosive/shorting salt spray on metal and insulators. Or exposure to
vandalism.
RX skimmers with a short antenna can be made very small, battery charged by
solar power, completely enclosed in smallish sealed box and communicating
with the internet via wifi back off the beach. They can be put on top of
pier poles, etc, and completely controlled remotely.
73, Guy
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|