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5
Rotator Unit Components and Dimensions
Tower-Mounted Antennas
In the preferred tower-mounting configuration, the antenna Wind Loading Area must be
less than
1m
2
, and the “
K
” factor (see below) must not exceed
100
, where
K
=
[Antenna
Turning Radius (m)] x [A Mast Weight (kg)]
.
Refer to the antenna manufacturer’s specification sheet for determining the turning radius
and weight of the antenna.
Example:
In this example, a 50 MHz 5-element Yagi of Turning Radius 2.5 m, Weight of
7 kg,and Surface area of 0.3 m
2
is proposed for tower mounting below a 3-ele-
ment 21 MHz Yagi of Turning Radius 4.2 m, Weight of 10 kg, and Surface Area
of 0.45 m
2
. The mast weight is 5 kg.
Note:
In such “Christmas Tree” installations, compute the mast weight separately for each
antenna, using the relative heights of the two antennas to apportion the mast weight.
The antenna system
K
factor, then, is the sum of the two antenna
K
factors:
K
1
=
K
factor of 50 MHz 5-element Yagi.
K
1
= Turning Radius (2.5 m) x Weight (4.5 kg + 2.5 kg) = 17.5
| |
Antenna Weight Mast Weight (5 kg ÷ 2)
K
2
=
K
factor of 21 MHz 3-element Yagi.
K
2
= Turning Radius (4.2 m) x Weight (7.5 kg + 2.5 kg) = 42.0
| |
Antenna Weight Mast Weight (5 kg ÷ 2)
K
Total
=
K
1
+
K
2
= 175. + 42.0 =
59.5
The antenna system Wind Loading Area is:
0.3 m
2
+ 0.45 m
2
=
0.75 m
2
The Wind Loading Area and “
K
” factor are within the specifications for the G-450ADC/
-450CDC.
Table 1: Wind Loading Areas for Common Antennas (Typical)
Band
(MHz)
Elements
Area
(m
2
)
Band
(MHz)
Elements
Area
(m
2
)
7
2-element
2.2
14/21
3-element, trapped
0.4
7
1-element, w/loading coils
0.2
14/21
4-element, trapped
0.5
7
2-element, w/loading coils
0.5
21/28
4-element, trapped
0.3
7
3-element, w/loading coils
1.1
21/28
5-element, trapped
0.4
14
3-element
0.7
14/21/28
3-element, trapped
0.4
14
4-element
1.2
14/21/28
4-element, trapped
0.5
14
5-element
1.7
50
4-element
0.25
21
3-element
0.45
50
5-element
0.3
21
4-element
0.6
50
6-element
0.37
21
5-element
0.8
50
2-element, Swiss Quad
0.3
21
6-element
1.3
144
10-element
0.2
21
2-element, Swiss Quad
0.3
144
10-element, stacked
0.44
28
3-element
0.3
144
10-element, x 4
0.95
28
4-element
0.42
144
10-element, x 4 x 2
2
28
5-element
0.6
430
12-element
0.06
28
2-element, Swiss Quad
0.3
430
12-element, stacked
0.12
7/14
3-element, trapped
0.5
430
12-element, x 4
0.3
7/14
4-element, trapped
0.8
430
12-element, x 4 x 2
0.6