[TowerTalk] Holy SteppIR!

[Jim Lux]

At 02:24 PM 12/26/2005, Michael Tope wrote:

>----- Or
> > he'll be able to pick the elevation that works best for any contact.
> >
>
>Interesting, Clay. I went back and looked at the pictures more carefully
>and indeed it looks like he has elevation control as well as azimuth. As you
>point out, this will allow him to adjust the take-off-angle. What it won't
>give him is the broad vertical lobe fill that you get from an optimized
>stack,
>so it will still be a compromise for contesting. For DXing, assuming he
>gets it pointed correctly, he should be the first guy through most of the
>time. Really puts my inverted-vees at 60' to shame. Guess I should have
>listened to an early engineering mentor who suggested that I should become
>a chiropractor :)

I would imagine that he can synthesize almost any sort of pattern he 
wants.  It's not just a matter of stacking Yagis and doing the BIP/BOP 
thing.  He can theoretically tune the upper and lower antennas a little bit 
high or low and get essentially arbitrary phase shifts, not to mention the 
effects of tuning the parasitic elements.

Mind you, figuring out the tuning (and then verifying that it actually did 
what you think it does from the model) is non-trivial.  However, he's got 
27 independent variables to fool with, and at least with Yagis far in the 
air, the oddball interactions are small, and so, something like NEC can 
model this quite effectively.

There's a lot of papers just recently in IEEE Trans on Ant and Prop that 
talk about ESPAR arrays, which have a central driven monopole, and a ring 
of 6 parasitic elements around it.  There are variable reactances connected 
to the parasitic elements, and they form beams, etc., by changing the loading.