[TowerTalk] Stacks (optimizing gain at takeoff angle)

[K3BU@aol.com]

Interesting subject.

Question is how N4NO "analyzed" the boom tilt angle effect, was it by 
software or by experimentation with real antennas in real situations?

VHF operators know that it helps if the beam is tilted up about 10 - 15 
degrees.
When I was experimenting with Razor designs, I found that if antenna was 
elevated to different height I could get better results by reconfiguring 
(optimizing) the spacing. So it appears that antenna should be designed for 
the height intended to be used at. (Probably some multiples of quarter wave 
would repeat?)
I have not tried to tilt the boom on HF antennas. But from the above 
experience it appears that antenna should be designed for the height and 
tilt. I wonder if anyone has done any testing.

Yuri, K3BU


In a message dated 8/20/2000 8:19:19 AM Eastern Daylight Time, n4kg@juno.com 
writes:

> Long ago, some people thought there might be an advantage
>  to mounting the boom of an antenna at the angle corresponding
>  to the desired takeoff angle.
>  
>  My mentor, N4NO, analyzed this and came to the conclusion
>  that such an installation actually produced LESS signal at
>  the desired angle.
>  
>  Let us consider a high takeoff angle of 30 degrees which
>  will emphasize the variations to make them more visible
>  to the naked eye or immagination.
>  
>  Picture the antenna pattern in the vertical plane.  As the 
>  boom is rotated up, there is a small increase in gain from
>  30 degrees to the axis of the boom (0 degrees).
>  
>  BUT, as the boom is rotated up, there is a LARGER DECREASE
>  in gain at the ground reflection angle where the angle to the boom
>  varies from 30 degrees to 60 degrees.  
>  
>  The COMBINED signal from the incident wave plus the ground
>  reflection will be LESS for a boom in-line with the desired
>  angle than for a horizontal boom which illuminates the 
>  incident angle and the ground reflection angle equally.
>  
>  de  Tom  N4KG
>  

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