On Tue, 27 May 1997 09:21:19 -0400 (EDT) "Charles H. Harpole"
<harpole@pegasus.cc.ucf.edu> writes:
>Help me here, but if grnd screen has no effect on HF Yagis, then why
>is
>height above gnd important to Yagis ? de K4VUD
Height above the REFLECTION POINT determines the angle of
radiation.
For LEVEL ground, that is the same as the height of the antenna
above
the ground underneath, but, there is (almost) NO USEFUL
reflection
from the ground directly underneath a horizontally polarized
Yagi,
especially on the higher bands and therefore ground screens under
the tower provide no benefit to high band Yagi's. The
reflection zone
will be from 2 to 10 times the tower height for most useful
angles of
radiation. - de TOM N4KG
>On Mon, 26 May 1997, T. A. Russell wrote:
>
>> Two things come to mind:
>>
>> First, a ground screen does nothing for HF Yagi's (for two reasons)
>>
>> a - A Yagi has a NULL straight up and straight down
>>
>> b - The GROUND REFLECTION point is hundreds of feet from
>the
>> tower
>>
>> Second, a ground screen WILL benefit any VERTICALLY polarized
>antenna on
>> or around the tower, but may rust out in a few years. My galvanized
>> electric
>> fence wire radials were heavily rusted in 3 to 5 years. The ground
>> reflection
>> from your quarter wave slopers is likely to be beyond the range of
>your
>> screen.
>> A shunt fed tower for 160M would benefit from the ground screen.
>>
>> de Tom N4KG
>>
>>
>> --
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>http://www.contesting.com/towertalkfaq.html
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>>
>
>
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