Cool idea, Jim. Not sure you could steer the elevation pattern enough to be
meaningful though. I just modeled a pair of yagis stacked 60ft apart (using
the 20m 5 el yagi that comes with EZNEC 3) and adjusted the driven-element
length 20 inches long on one yagi and 20 inches short on the other. This
only steers the takeoff angle up by one degree.
Very interesting idea though...
73 - Bryan W4WMT
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of Jim Lux
Sent: Thursday, September 11, 2003 4:22 PM
To: k2hk@arrl.net; kg6i@direcway.com
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Stacked 4 El SteppIR's
Theoretically (horrible word that, sometimes), you could do some
interesting stuff by deliberately tuning one driven element a bit long and
the other a bit short. When combined, they'll have a good match, but one's
phase will be shifted relative to the other. This would allow you to scan
the main lobe in elevation, which might be useful, particularly on a high
angle path.
It also might let you put a null at some particularly annoying elevation
angle (probably the more useful feature).
Mind you, I have no idea how you'd go about adjusting all the other
elements in a practical way. One could have some sort of modeling program
with an optimizer, the output of the modeling program used to drive the
element actuators. The real problem, as I see it, is that there's often a
great difference between model and reality, and, then, between what you
think is the optimum pattern, and what actually is.
Getting it to be fast enough to be convenient would also be tricky. Even
on a fast computer, optmizing the yagi element lengths takes some amount of
time.
Perhaps a better approach would be to precalculate element configurations,
and then have another (virtual) knob that sets elevation, along with the
rotator knob to set azimuth.
Think of it as a control box for 8 elements instead of just 4.
Jim, W6RMK
_______________________________________________
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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