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Re: [TowerTalk] 80 Meter Delta Loop

To: towertalk@contesting.com
Subject: Re: [TowerTalk] 80 Meter Delta Loop
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 23 Jul 2024 15:50:19 -0700
List-post: <mailto:towertalk@contesting.com>
On 7/23/2024 2:48 PM, RVZ via TowerTalk wrote:
  Please advise if there would be much advantage with replacing my 80-m.
Inverted Vee with apex at 100' AGL with a full-wave 80m. Delta Loop with
  apex at the same height and fed at the top? Note: I realize the Delta
Loop would have a lower angle of radiation if it was fed at a bottom
corner but that isn't possible at this QTH.

NEC modeling should give the answer if you enter the soil parameters for your QTH. I've found NEC to be quite accurate if the model accurately describes the antenna.

One VERY important part of correctly comparing the antennas is to save H and V plots of their patterns, then import them on corresponding plots of the other antenna. This will cause the amplitude scale to be the same for both antennas. Otherwise, we're fooled by the so-called "take-off angle," which is a terrible way to describe an antenna.

One of the most common fallacies promoted by "take-off angle" is that a ground-hugging horizontal dipole is optimum for NVIS. Reality is that the optimum height of a horizontal dipole for NVIS is a quarter-wave.

For an example of what I'm talking about, study this modeling study I did about ten years ago. NCJ wanted to publish it, but the publishing folks at ARRL nixed it because there was too much graphics (which was absolutely necessary to show the result)! Here's the NCJ piece.

73, Jim K9YC

http://k9yc.com/AntennaPlanning.pdf



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