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Text File
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1991-08-31
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2KB
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49 lines
SUBJECT: Attic VHF/UHF Rotatables
In many instances, a ham can mount a VHF or UHF beam in the attic, on
a rotor. They can achieve good results depending on their location and
height off the ground. Antenna size limitations are soley dependent on
the available room in the attic that allows rotation of the beam without
hindering it's rotation.
To check the attic for the maximum size antenna, the ham must first
enter the attic and measure the distances in the area planned for the set-up.
Trusses, electrical wiring, air conditioning / heating ducts, and the items
that are stored up there, can all play a factor in the actual antenna size.
Finding your antenna with a pair of long johns dragging off the front
end is not a pretty sight.
After measuring the area in the attic, the antenna size and height off
the attic cross members can be accomplished. Remember to allow for a base
to accommodate the rotor. This too must be calculated into the system.
Building a sleek system, to rotate two or three small beams, can be
dashed, when the system will not turn because of an oversight in the
measured values of the attic area in question.
Turning radius is the important factor. Each antenna forms a
rectangle ABCD where the maximum distance is AD or BC.
A------------------------------------B
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----|----------------------------------|---- BOOM
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C------------------------------------D
For horizontal antennas, the turning radius is from the mounting
point to the tip (either side) of the longest element. Multiple this figure
by two for the turning diameter of the antenna.
For vertical antennas, the truss angle places the biggest problem
as the height from the boom to the tip of the refector (B or A). In essence,
this will shorten your boom length or require a lower rotor mounting.
These tips will help the Amateur avoid any problem before
getting the system in the attic.
-WS