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Re: [TowerTalk] Antenna eating tree

To: "" <>
Subject: Re: [TowerTalk] Antenna eating tree
From: "Jim Brown" <>
Date: Sun, 03 Sep 2006 11:35:32 -0700
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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 
in HFTA. 

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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