Site preparation
3-6
Chapter 3: Installation
98-166784-A
3.2.4
Safe access to the ADU (radiation hazard)
The ADU radiates radio frequency energy at a level below the United States FCC radio
frequency exposure limits. Nevertheless, caution should be taken to minimize potential for
RF exposure to human. Make sure to turn off power to the ADU before removing the
radome and working on the antenna.
3.2.5
Ship motion and offset from the ship’s motion centre
When installing the ADU you must consider the mounting height carefully. The higher up
the ADU is mounted, the higher is the linear g force applied to the ADU. The g force also
depends on the roll period of the ship, see Table 3-1. If the g force applied is too high,
performance and ADU signal stabilization may be reduced and eventually the ADU may be
damaged. See the following table for allowed mounting heights above the ship’s motion
centre.
Even though it is recommended to mount the ADU high, keep the distance between the
ADU and the ship’s motion centre as short as possible.
Figure 3-4: Maximum distance from the ship’s motion centre (h max)
Min.
roll period
Maximum antenna mounting height (h max)
Full performance
Potential risk of damage
4 s
12 m (39 ft)
16 m (53 ft)
6 s
27 m (89 ft)
35 m (115 ft)
8 s
48 m (158 ft)
62 m (203 ft)
10 s
75 m (246 ft)
98 m (322 ft)
Table 3-1: Maximum distance from the ship’s motion center versus
ship’s roll period
h max
