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Re: [TowerTalk] HFTA Accuracy / Usefulness

To: TOWERTALK@contesting.com
Subject: Re: [TowerTalk] HFTA Accuracy / Usefulness
From: Cqtestk4xs@aol.com
Date: Wed, 18 Mar 2009 13:53:18 EDT
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I'm not an engineer, or antenna designer...just a contester and kind of an  
"appliance op".
 
Back in Florida, I used antenna stacking programs and did not concern  myself 
with HFTA since most of Florida is pretty much like a table.  When I  moved 
to KH6, it was a different world.  On my three acres there is a drop  of almost 
150 feet, the vertical drop over the next 3500 feet to the ocean  is over 800 
feet.  There are big gulches that drop 500 feet within 300  feet of the 
antenna.  In another direction it is almost flat for 1000  feet.   You get the 
idea....HFTA was a must.
 
I modeled the current set up using the HFTA program by N6BV which is in the  
ARRL Antenna Handbook.  The set up is on a 150 foot tower and has a stack  of 
3 tribanders at 92, 56, 29 and two 4 el 40 meter Yagis at 150/80...all  
heights modeled from Dean's program.  I could have put the tribanders at  
greater 
heights if I wanted, but I didn't. In the 18 months I've used the stack  
designed from that HFTA, I've won lots of contests and even set some  records.  
The 
program works.  Just using your intuition may or may not  result in a killer 
antenna set up.  This program gives you a better chance  in accomplishing that 
killer system.
 
I'm weak where the program said I was weak...to the south looking up 13500  
foot Mauna Kea volcano and to VK/ZL which also goes up hill..  And, I'm a  
beacon into EU, which is just what the program predicted if I used the graphs  
correctly.
 
If you're on flat ground don't waste your time with the program, but if you  
are on a hilly terrain it's priceless.  I don't intend to move my antennas  to 
different heights to check my results.  They might work better at  different 
heights, but I don't really want to invest the time to find out.
 
Something to note though...As Dean states, the gain from stacking antennas  
tends to get a little sticky when the antennas in the stack start to get below  
1/2 wavelength in spacing, giving higher than normally expected gain.   Aside 
from this caveat, which is just common sense, this program is 10 out of  10.  
Once you have your terrain tables the program is easy to  use.  Be sure to 
look at the arrival angles when using the program and  focus on the fig. of 
merit.  No height will be perfect but you'll be able  to pick the best one for 
overall use.
 
73 Bill KH7XS/K4XS
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