[TowerTalk] Stacks (optimizing gain at takeoff angle)

[Saul Abrams]

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
-----Original Message-----
From: K3BU@aol.com <K3BU@aol.com>
To: TOWERTALK@contesting.com <TOWERTALK@contesting.com>
Date: Sunday, August 20, 2000 10:16 AM
Subject: Re: [TowerTalk] Stacks (optimizing gain at takeoff angle)


>
>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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