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Re: [TowerTalk] Height for 40m yagi

To: "Kjeld Holm" <>, <>
Subject: Re: [TowerTalk] Height for 40m yagi
From: "Al Williams" <>
Date: Sun, 16 Apr 2006 07:50:21 -0700
List-post: <>
----- Original Message ----- 
From: "Kjeld Holm" <>
Sent: Sunday, April 16, 2006 1:28 AM

> Can any Yagi for 40m do any good at a height of 27 feet (on a 130 feet 
> hill
> top)?
> Or do I have to stay on 20m and above with this  height limitation?

This a question that antenna modeling programs can be of great help.  I have 
been using EZNEC the last few days to try to determine how to improve our 
field day 40m antenna installation.

To answer your question, IT DEPENDS!
1. What is your opinion of "good"?
2. What configuration of Yagi?
3. What is the hill top like?
4. What is your 40m reference e.g. no 40m capability or a dipole at same 

3. I don't have experience with Terrain Analysis, but from what I have read, 
the hill top unless very, very steep fall off from your antenna will have 
little effect on the radiation pattern.  (As far as being "good" is 
2. Our 3 element fixed azimuth field day wire yagi when modeled at 27 feet 
high shows a very worthwhile gain over a dipole at the same height.  While a 
dipole at that height is at the upper height range for a NVIS antenna 
(meaning that the maximum radiation is straight up), the 3 element beam 
elevation radiation is definitely skewed away from straight up and has a 
elevation maximum radiation at 48 degrees. At this angle the beam has a gain 
of 8.34 dbi and about 3 db gain over a dipole.  At 30 degrees elevation 
angle the yagi gain is 7.09 dbi while the dipole is down about 4 db from the 
dipole.  At 15 degrees elevation, the yagi gain is only 2.72 dbi but the 
dipole is down again about 4 db.
1. If your opinion of good is to be able to make more distant contacts on 40 
(but not much dx) then the gain of the yagi along with the capability to 
rotate makes a very worthwhile improvement.  On-the-other-hand, installing a 
40m yagi and rotator is a lot of work and expense and if your "good" is 
making short range contacts then a simple fixed dipole at about 20' high 
would be quite satisfactory.

Either choice gets you on the air on 40, thus could be considered good!

I hope this helps--my advice, consider obtaining an antenna modeling 



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