Re: [TowerTalk] Stacked 4 El SteppIR's

[Jim Lux <jimlux@earthlink.net>]

At 07:28 PM 9/11/2003 +0000, Howard Klein wrote:
> Hi John,
> Right you are.  I am out of town and forgot the exact boom picture. I know 
> I was not very disturbed over the boom specs. I actually got my 2nd 4 el 
> up Sunday but before I had time to tune the pair I had to leave town. I 
> can only say I am extremmely impressed with the top 4 at 75 ft. The lower 
> at 40ft (right now) sounds pretty good also. I need to play with the 
> separation and tune the individual antennas when I get home to see how the 
> stack will work. It's hard to believe that it can only get better. Good 
> <uck to John.
> 73,
> Howard..K2HK

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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