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Re: [TowerTalk] 15m monster finally up

Subject: Re: [TowerTalk] 15m monster finally up
From: Jim Lux <>
Date: Wed, 26 Sep 2012 16:14:12 -0700
List-post: <">>
On 9/26/12 10:16 AM, wrote:
After studying this a little more, I do not think that the beamwidth can
be easily changed with switching.  In a model I tried driving only one
side of the array and the pattern looked similar to the fully driven
stack, just slightly skewed. One thing for sure, this will be very very
strong in the direction it is pointing.

Very interesting

I just ran a quick model using a 3 element Yagi (from Cebik.. it's the sample with 4nec2 called 3lyagi20) I duplicated it 50 feet over (the driven element is about 34 feet long)

With both driven, gain is 16dBi, HPBW in the horizontal plane is 40 degrees

With one driven, the other shorted (E=(1E-5,0)) the gain is 13.11 max at 4 degrees towards the shorted element, HPBW is 70 degrees

With one driven, the other open, the gain is 9.34 dBi, pointed 8 degrees away from the undriven antenna), HPBW is 70 degrees

With the undriven antenna shorted, the gain is almost exactly 3 dB less, pretty much what I expected.

All I can figure is that with the driven element open, the reflector and director are still coupled to the original antenna, and sucking some power away, and reradiating it with a bad relative phase.


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