At 02:35 PM 12/27/2005, Michael Tope wrote:
>----- Original Message ----- From: "Jim Lux" <jimlux@earthlink.net>
>To: "Michael Tope" <W4EF@dellroy.com>; "Joe Subich" <W4TV@subich.com>;
>"'StellarCAT'" <RXDesign@ssvecnet.com>; "'tower'" <towertalk@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@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)?
It is a mindboggling problem, but one that a few hours of modeling and
experimentation could probably answer. You'd certainly not want to try and
do this with EZNEC or 4NEC2 or one of the graphical front ends. You'd
probably want to write some scripts to generate NEC decks, fire off the
engine, and extract the relevant data. Much like that nifty stuff with
optimizing view angles using Perl, etc. in QEX a few months/years ago.
>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?).
Yes, but....
There's no easy answer (as in a "rule of thumb" that says, with N elements,
you can get Y width main lobe and Z width null)
Jim..
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