Topband: Fwd: Unique Short Radial Challenge
btippett at alum.mit.edu
Mon Oct 22 19:03:06 EDT 2007
---------- Forwarded message ----------
From: "Dave N2NL" <daven2nl at gmail.com>
To: topband at contesting.com
Date: Mon, 22 Oct 2007 18:53:35 -0400
Subject: Re: Topband: Unique Short Radial Challenge
>Oh "DUH!"- I just realized if I had bare copper wire running out across the
>rocks and weighted down just below the water a low tide, as the water level
>increased, there would *always* be some connection between water level and 7
>inches beneath it :-) Hopefully it would not corrode/erode beyond
>uselessness in the 3 days I only need it for.
>Tnx & 73...
My apologies if my weigh in is late - I've been away from
internet access the past few days.
I have some real-life experience with antennas over salt water.
>From '03-'05, I was stationed here in Key West and experimented with
several verticals located on and around my dock. Before reading some
posts from W8JI regarding skin depth, I strung several hundred feet of
radial wire out in the flats, submerged perhaps 2-3ft deep in salt
water. I also had several radials running through the mangroves,
slightly above and below the water line.
In every case, I had difficulty matching the vertical and
performance was marginal at best. Although the tidal range here is
less than 2 feet, I noticed significant SWR fluctuations as the water
level rose and fell. In every instance, my R-7 "no radial" vertical
out performed every other 1/4 wave vertical with lots of radials in
salt water. It was a frustrating lesson.
A few months ago, I was transferred back to Key West and live
about 6 houses down the same street, also with a dock. This time, I
did some research, reading posts from W8JI and K2KW. I recommend you
read through Ken's web site:
This time, I mounted 1/4 wave verticals and used elevated,
insulated radials. Details can be found here:
The performance of these antennas is outstanding. I truly feel
loud on 40 and 80, and to a lesser extent, 160m. Would 16 or 32
elevated radials work even better? Perhaps, but I'm limited to what
I've got now. Antenna modeling with EZNEC shows no difference in
radiation angle and pattern when modeled with only one, two, or 16
radials in this configuration, using the generally accepted values for
salt water conductivity (5.0/81). I suspect the effort to string more
radials would far exceed the resulting performance gain over what I
have now, not counting the possibility of upset neighbors.
Your mileage may vary. Rick, in your case, being as close to
lossy ground (rock) as you are, a couple elevated radials likely would
not work as well as a vertical with salt water in all directions. I
recommend as many radials over ground as possible, with as much wire
suspended over the water as you can. Chucking some wire in the water,
even a few inches deep, will give you a good earth ground but likely
won't help very much as a return path for RF.
73, Dave N2NL/4
More information about the Topband