Hi Eric and Gang,
Eric, your point about the fallacy in my thinking between parasitic array
and driven array is well taken. I'm sure you're right. I dug out some of my
antenna books today and did some reading on the log periodic.
The reason i only considered the T-6 is because my tower is a Rohn 25G and
i live in hurricane alley. The Rohn specs. for 110 mph call for windloading
not to exceed 8.3 sq.ft. Allowing a little for a rotator and mast, i don't
want to go much beyond 7 sq. ft. Even then theres a possibility that the
wind it could be subjected to may easily exceed 110 mph. Had hurricane Floyd
not de-intensified so quickly , it could have brought us winds exceeding
120-130 mph. If course, hopefully in that instance the antenna would give
its life to save the tower.
Several months ago i modified my posture on the parameters concerning my
tower, thanks to advice i received here. I not only met specs wherever
called for, in some cases i exceeded them. For instance, when i laid the
tower guys out i put one guy in the Northeast and that is where the highest
hurricane force wind will likely come from. When i poured concrete, i had
twice as much poured as necessary. When i learned that i would need to break
up the guys with insulators, in order to shunt feed the tower, i ordered
enough insulators and preforms to do it every 13-14 ft. along the length of
both levels of guys. Thanks for all the advice from everyone.
Although i thought about it, i've decided to continue to be patient and
just order the F12 C3SS and wait. With perhaps one exception, HRO doesn't
stock F12, nor First Call, nor Texas Towers. I'm told that the profit margin
is too slim to do so.
I wish i had the resolve to do like one W1 i read about who didn't worry
about having but one antenna, or at least one yagi, a monoband 20 meter job.
His reasoning? All DX comes to 20! Can't argue with that! Ha! :o) I guess i
want all the bands ! And all the gain i can get consistent with relatively
small size.
73 all, de Roy Lincoln WA4DOU
------------------------------------------------------------
On Sat, 2 Oct 1999 11:40:29 -0700, Eric Gustafson wrote:
>
>
> Hi Roy,
>
> See my comments below.
>
> >From: wa4dou@juno.com
To: <towertalk@contesting.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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