[TowerTalk] Fwd: [CQ-Contest] Stacking on separate towers, take off angles?

[Hans Hammarquist]

Driving several yagis located next to each other and get a predicable result is not that hard. You "just" have to phase them correctly and point them in the direction your resulting wave front is going This has been done for many years in certain RADAR installations. 


You don't even have to be that precise with the phase angle at each antenna, 1/8 wavelength is well enough.


If you have an installation there the antennas are lined up on a straight line and you feed each antenna is phase with the rest you main lobe will be perpendicular to the line. If you delay the feed to the antennas to the right, looking in the direction of your main lobe, the lobe will start to bend to the right. The math is rather simple even if it sounds complicated when you try to write it down. My suggestion, if you want to study it a little deeper, start looking for "diffraction" such as http://en.wikipedia.org/wiki/Diffraction . That gives you some ideas.


Hans - N2JFS



-----Original Message-----
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk <towertalk at contesting.com>
Sent: Sat, Mar 16, 2013 10:55 am
Subject: Re: [TowerTalk] [CQ-Contest] Stacking on separate towers, take off angles?


On 3/15/2013 8:19 PM, David Gilbert wrote:
> No way that the respective wavefronts will add in all of those 
> directions.  Geometry alone would tell you they are much more likely 
> to cancel in some directions. 

Right. MANY directional arrays are the result of wavefronts from 
multiple driven elements that add algebraically (magnitude and phase) 
differently in different directions and elevation angles. Magnitude and 
phase of any antenna varies with both horizontal and vertical angle, and 
antennas will have some magnitude and phase relationships to each other 
based on their  spatial relationships.

Yes, we can drive two or three Yagis pointed in the same or different 
directions, but HOW they combine to form a pattern can be as close to 
the infinite number of monkeys and typewriters as it is to how the 
operator thinks he is aiming them.

73, Jim K9YC
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