[TowerTalk] Holy SteppIR!

[Michael Tope]

----- Original Message ----- 
From: "Jim Lux" <jimlux at earthlink.net>
To: "Michael Tope" <W4EF at dellroy.com>; "Joe Subich" <W4TV at subich.com>;
"'StellarCAT'" <RXDesign at ssvecnet.com>; "'tower'" <towertalk at contesting.com>
Sent: Tuesday, December 27, 2005 9:46 AM
Subject: Re: [TowerTalk] Holy SteppIR!


> At 08:02 AM 12/27/2005, Michael Tope wrote:
>
>>----- Original Message -----
>>From: "Joe Subich" <W4TV at subich.com>

>>Yeah, that sounds about right. Below that level, the vertical pattern
>>nulls shouldn't be affected too much (if at all) by the "tilt".
>
>
> Assuming you didn't phase the elements to create a null at the ground..?
> With a SteppIR, there's no requirement that the antennas in the stack will
> be radiating at the same phase.  You can arbitrarily adjust the phases, so
> you can put a null wherever you want. In fact, it's easier to place nulls
> than to place lobes.
>
>

Yes, that's absolutely right, Jim. I am guilty of thinking "in the
box". If you remove the straight jacket of the conventional Yagi
with fixed tuning/phasing, and exploit the large design space
allowed by the independent element length control, you can
probably do some interesting things. It would be an interesting
study to figure out the various possibilties for elevation pattern
control. You could then feed that information to the SteppIR
controllers to get an electronically steerable elevation pattern.
I wonder if this is what the owner has in mind (maybe he isn't
as misguided as we first thought)?

Still, even when you open up the possibilities afforded by
arbitary element length control, it is not clear to me that you
can achieve as clean an elevation pattern as a conventional
vertical stack in the range of interest (say 3 to 15 degrees
TOA). Even if you synthesize nulls looking toward the ground
at a specific angle, you still are fighting the grating lobes that
want to form at other angles due to the large spacing between
the array and the ground image (e.g. can you cut down the
ground illunimation over a broad range elevation angles without
cutting down the corresponding direct radiation and achieve a
broad main lobe close to the horizon?).

73, Mike W4EF...............................