Site considerations
98-175666-D Chapter 2: Installation 2-5
2.2.2 Obstructions (ADU shadowing)
The ADU beam is approximately 1 m in diameter for the first 30 m from the ADU.
Beyond 30 m the beam gradually widens so that it is approximately 5 m in diameter at
100 m distance. This beam expansion continues with increasing distance. Any
obstructions, such as masts, funnels, bridge house etc. within this field can cause
signal degradation or signal loss.
For optimum performance adhere to the following guidelines:
1. Place the ADU so that it has as much free line-of-sight to the satellite as possible
without any structures in the beam through one full 360 degrees turn of the vessel.
2. Do not place the ADU close to large objects that may block the signal.
3. Elevate the ADU by mounting it on a mast or on a mounting pedestal on a deck or
deck house top to avoid obstruction.
Note
Due to the short wavelength at Ka band and the narrow beam width of the
ADU even a 6 mm steel wire placed within 50 m inside the beam can
causes signal degradation.
Figure 2-2: Signal degradation because of obstructing objects, look angle -18° to 118°
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