[TowerTalk] Stacks (optimizing gain at takeoff angle)

[i4jmy@iol.it]

If the direct wave increases, the reflected wave does exactly the same. 
All the point with horizontally polarized yagi HF antennas is in the 
phase realtionship, at a distant point, between the direct and the 
ground reflected wave. 
If the explaination of "greater amount" were true, gain apart, deep 
nulls on vertical pattern (the result of same amplitutde but 180° phase 
shift between direct and reflected waves) could be replaced by a 
consistent radiation (up to the antenna free space gain) without 
varying antenna height but symply by properly tilting an antenna with a 
small aperture on the vertical plane, just enough to reduce the 
unwanted reflected wave for a stated elevation and so "killing" the 
null.
Unluckyly, things are different and the antenna height must vary to 
fill nulls in the vertical plane.

73,
Mauri I4JMY




> ---------- Initial message -----------
> 
> From    : owner-towertalk@contesting.com
> To      : <K3BU@aol.com>, <TOWERTALK@contesting.com>
> Cc      : 
> Date    : Sun, 20 Aug 2000 20:14:32 -0400
> Subject : Re: [TowerTalk] Stacks  (optimizing gain at takeoff angle)
> 
> 
> 
> Chapter 5, Section 5-14, Antenna Tilt, of "Yagi Antenna Design" by 
James
> Lawson, W2PV says:
> "Unfortunately, tipping the antenna upward automatically tips the 
image
> downward by the same angle; the net result is that, while the direct 
wave is
> increased, the reflected wave is decreased, and by a greater 
amount."  73
> Saul  K2XA



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