On Thu, 3 Apr 2008 19:00:47 -0400, "Bob Crantz"
wrote:


"Goofball_star_dot_etal" wrote in message
news
On Wed, 2 Apr 2008 13:10:05 -0600, "Bob Crantz"
wrote:


"Wilbur Hubbard" wrote in message
. octanews.com...
I have personal experience with respect to this topic. Putting a wi-fi
antenna at the masthead is the WRONG thing to do. You don't want it high
up. You want it low down. It gets better reception low. The signals seem
to be stronger low. Mount a good amplified antenna at deck level for the
best reception. No need to worry about long lengths of co-ax at all.

Here's a good antenna that works well and is priced reasonably.
http://www.radiolabs.com/products/wi...ne-antenna.php

Wilbur Hubbard


If your antenna is vertically polarized you could see a 3 dB increase in
signal if it placed over a conducting ground plane such as salt water.

6dB. Principle of superposition. No power splitting required for the
image. No change in antenna radiation impedance if the distance from
antenna to ground plane is large in terms of wavelengths,
as is likely to be the case in this situation.



It's 3 dB in power and it's the Principle of Images that is used to remove
the ground plane and locate a virtual mirror image of the antenna. The
Principle of Superposition is used after the Principle of Images to
calculate the field. One would tend to say it's 6 dB in voltage but that is
misleading as the input impedance varies between the real and image and it
is power (actually energy) that is conserved. You're right about the spacing
being important.

Glory!


It is not just a question of squeezing the energy from a sphere into a
hemisphere. If the antenna and its image are separated by a number of
wavelengths nulls occur in the polar plot, so that you cannot simply
claim that a gain of more than 3dB violates the Conservation of
Energy. Principle of Superposition rules. Amen!