[TowerTalk] 15m monster finally up

[Jim Lux]

On 9/26/12 10:16 AM, john at kk9a.com 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.