On Sun, 03 Sep 2006 13:56:41 -0400, Jim Jarvis wrote:
>replace ALL the antenna with heavier wire, or, try something
>completely different, for 160. Intriguing question.
Faced with a similar problem, I've been spending lots of time with
the ARRL Antenna Book. The later versions have some interesting
thinking on the topic of wires, and the vertical radiation
patterns of antennas at various heights above terrain.
The editor of the Antenna Book, N6BV, is president of a ham club
that I belong to here in the Bay area, and is the author of the
HFTA program that predicts vertical angle of radiation as a
function of the terrain and antenna height. Members of that club
are serious contesters and DXers, and are pretty strong believers
As data for the program, you plug in contour data that can be
pulled manually, point by point, from topo maps, or downloaded in
digital form from a USGS website. I've done both, and the USGS
method is definitely the way to go. :)
I've been spending a lot of time with HFTA over the past few
weeks, and am learning a lot from it. It's including on the CDROM
that comes with the 20th version of the Antenna Book (the current
one). The CDROM also includes software that converts the USGS data
to the radial contours that HFTA needs.
At my new QTH, I'm about 200 ft below the top of a couple of
ridges that run from roughly 320 degrees azimuth to about 190
degrees. It should come at no surprise that the relationship
between antenna height and vertical radiation angle is a rather
complex one at my QTH.
Here's a pdf that I put together a week or so ago to solicit
advice from the NCCC guys. It illustrates the sort of output that
the software provides, and what you might expect from it at your
QTH. Note also that the model upon which HFTA is based applies
specifically to horizontally polarized antennas.
One additional thought, Jim. One antenna I will definitely have up
and running this fall is the west coast version of the top-loaded
vertical detailed on my website. Here in CA, I'll have it about
twice as high (thus with a much higher vertical portion), and a
nice radial system under it. Like the Chicago version, I plan to
run it on 80 and 160 as a supplement to horizontal dipoles for
those bands. In Chicago, it worked fairly well considering its
more limited implementation (and was the only way I could work 160
from that QTH).
Jim Brown K9YC
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