l Tower-Mounted Antennas
In the preferred tower-mounting configuration, the antenna Wind Loading Area must be less than 1
m
2
(G-450A) or 2 m
2
(G-650A), and the “K” factor (see below) must not exceed 100 (G-450A) or
180 (G-650A), where K = [Antenna Turning Radius (m)] x [Antenna + Mast Weight (kg)].
Refer to the antenna manufacturer’s specification sheet for determining the turning radius and weight
of the antenna.
In this example, a 14 MHz 3-element Yagi of Turning Radius 7.5 m, Weight of 14 kg,
and Surface area of 0.7 m
2
is proposed for tower mounting below a 3-element 21/28
MHz trapped Yagi of Turning Radius 3.5 m, Weight of 13 kg, and Surface Area of
0.3 m
2
. The mast weight is 5 kg.
Note: In such “Christmas Tree” installations, compute the mast weight separately for each an-
tenna, 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 14 MHz 3-element Yagi.
K
1
= Turning Radius (7.5 m) ´ Weight (14 kg + 2.5 kg) = 123.75
| |
Antenna Weight Mast Weight (5 kg ÷ 2)
K
2
= K factor of 21/28 MHz 3-element trapped Yagi.
K
2
= Turning Radius (3.5 m) ´ Weight (13 kg + 2.5 kg) = 54.25
| |
Antenna Weight Mast Weight (5 kg ÷ 2)
K
Total
= K
1
+ K
2
= 123.75 + 54.25 = 178
The antenna system Wind Loading Area is:
0.7 m
2
+ 0.3 m
2
= 1.0 m
2
The Wind Loading Area is within the specifications for both the G-450A and G-650A, but the net
K factor (178) can only be met by the G-650A. Therefore, the above antenna system should only be
mounted using a G-650A (or larger) rotator.
Note: Installation of a Thrust Bearing such as the GS-065 does not allow the elimination of the
mast weight from the K-factor calculations above.
Example
Mast Bearing GS-065 (option)
5
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