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Obstructions Around the ODU
The satellite signals received by the antenna are less then 45° above the local horizon 90% of the time.
Therefore, obstructions that impact signal reception must be considered prior to installation.
To ensure the best possible connection with the Iridium satellite network the ODU needs clear exposure, in all
directions, to the sky. Two types of obstructions that should be considered when deciding the placement of
the ODU include: metallic and building/fixed obstructions.
The loss of signal (dB) will increase the closer the obstruction is to the ODU. The table below shows the
correlation between the size of the obstruction and the distance of the obstruction from the ODU and the
amount of signal loss.
Obstruction Signal Loss Table – Signal interference around the ODU
Diameter of Obstruction
.2 m (.7 ft.)
.4 m (1.3 ft.)
.6 m (2 ft.)
.8 m (2.6 ft.)
1.0 m (3.3 ft.)
RADAR systems or high power transmitters may cause signal interference.
To avoid possible damage to the ODU and degradation of the ODU performance the unit must be mounted as
far away as practical from these units. In addition it should also be kept clear of other sources of interference
such as other Iridium or Inmarsat terminals.
The diagrams and tables below are only guidelines as the minimum distances will be dependent on the
exact transmitter characteristics as well as reflections from surfaces or other items in the vicinity of the ODU.
The tables for X and S-band radar distances are minimum distances to avoid damage to the ODU and do not
necessarily guarantee a good communication link.
Minimum Distance from S-band & X-band RADARs
S-band (- 10 cm / 3 GHz) radars
Radar Power
Min distance at 15˚ vertical separation
0 – 10kW
0.4 m (1.3 ft.)
30kW
1.0 m (3.3 ft.)
50kW
2.0 m (6.6 ft.)
Obstruction Distance
< 2 m (6.5 ft.)
< 4 m (13.1 ft.)
< 9 m (29.5 ft.)
< 31 m (101.8 ft.)
< 22 m (72.2 ft.)
< 75 m (246 ft.)
< 40 m (131.2 ft.)
< 65 m (213.2 ft.)
Signal Loss
2 dB
1 dB
2 dB
1 dB
2 dB
1 dB
2 db
1 dB
2 dB
1 dB
Min distance at 60˚ vertical separation
0.4 m (1.3 ft.)
0.5 m (1.6 ft.)
1.0 m (3.3 ft.)
Iridium Pilot Land Station Installation Guide
11
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