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Re: [TowerTalk] Takeoff angle

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Takeoff angle
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 23 Jul 2017 21:17:50 -0700
List-post: <mailto:towertalk@contesting.com>
I consider use of the words "takeoff angle" to be VERY misleading, and cause a LOT of misconceptions. It is common to use the words "takeoff angle" to define the vertical angle at which field strength is greatest, and that the antenna only works at that angle. Nothing could be further from the truth.

Several years ago, I presented a modeling study showing that the low angle radiation (15 degrees and below) of a horizontal antenna for 80 or 40 M continues to increase as the antenna is raised above ground. I showed this by ignoring where the peak of the vertical pattern was, instead looking only at the low angle field strength as the antenna was raised. I didn't look at the SHAPE of the pattern -- instead, I plotted curves of field strength at 5, 10, and 15 degrees as the antenna was raised. A similar study for 20M produces comparable results, taking wavelength into account. That study is presented in the link below, starting around page 10.

http://k9yc.com/AntennaPlanning.pdf

That study is, of course, for "flatland," where terrain is not a factor, but the same concepts apply in irregular terrain, except that the terrain shifts the lobes up and down.

73, Jim K9YC

On 7/23/2017 6:27 PM, Steve Maki wrote:
Err, we better keep straight whether we're speaking of heights above ground or takeoff angle.


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