[TowerTalk] Yagi versus Log Periodic

[Eric Gustafson]

Hi Roy,

See my comments below.

>From: wa4dou@juno.com
>Date: Sat, 2 Oct 1999 00:48:29 -0400
>
>Hi Guys,

Snip... (discussion of gain possibilities for various antenna
	 configurations) 


>The yagi depends on a driven element with parasitics nearby, one
>or more, tuned quite closely to the driven elements freq. The
>reflector is tuned about 5% lower, the director about 5%
>higher. At the risk of oversimplification, the log periodic
>covers perhaps an octave to an octave and a half in freq. The
>T-6 covers 13-30 mhz., or thereabouts. 6 elements in a 17
>mhz. bandwidth, must be spaced in freq. about 2.8 mhz.  from
>each other. It appears impossible to have any 2 elements in such
>proximity to each other so as to compliment each others tuning
>the way a 2 element yagi does. Therefore i find it impossible to
>believe that the 6 element 17 mhz. bandwidth T-6 can have more
>gain than a 2 element yagi.  Yet clearly the elements in the T-6
>must have some complimentary effect.

The fallacy in your comparison here is that you are comparing the
characteristics of a parasitic array with those of a driven
array.  What is possible in the LPDA is largely dependent on what
constraints are placed on boomlength.  Since the magnitude and
phase of the current in the elements is not dependent on mutual
coupling alone, the relative sizes and spacing of the elements do
not constrain performance in the same way that those parameters
would for a parasitic array.



Snip...  (usual call for useable gain standards for comparison
	  purposes -  which I second)

Snip...  (lament over relative availabilities of desired product)


>I still find myself thinking about cutting and running and
>ordering a T-6. After very patiently waiting for several months
>to complete several aspects of my tower project, and being held
>up for weeks lately by Hurricanes Dennis and Floyd, I'm
>beginning to feel a little impatient. I wish I could find a C3SS
>on the shelf, or even a C3S, or a C4S.

Why are you stuck considering only the T-6?  Why not the T-12?

73, Eric  N7CL

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