Line-of-Sight Requirements
Satellite Data Modem (SDM) Installation
8-4
MAY CONTAIN U.S. AND INTERNATIONAL EXPORT CONTROLLED INFORMATION
80-J4866-2 Rev. G
Line-of-Sight Requirements
• SDM requires an unobstructed line-of-sight view to the satellite in order to clearly send and
receive signals.
• SDM must be able to send and receive the signals at a 12° angle above the horizontal
plane of the unit. There must be an unobstructed view of the satellite at all angles above
12°.
The following illustration shows the 12° angle and the maximum allowable height of
objects located at various distances from the SDM centerline.
• An obstruction height of 2.5 feet for every 12 feet away from the SDM centerline is
acceptable. Use this same formula to verify that a trailer hooked up to the vehicle does not
extend above the 12° angle.
• Satellite signal can normally pass through thin layers of glass, fiberglass, and plastic. Thick
layers or obstructions above the 12° angle may block the satellite signal and cause “blind
spots.” Keep blind spots to a minimum:
- Multiple layers of fiberglass, glass, or plastic
- Areas with numerous bends in the fiber glass
- Metal and wood bracing
- Metallic paints and lead-based paints
- Company logos that contain metallic materials
- Metal airdams, metal wings, metal side skirts, air conditioning units, and exhaust
stacks.
• When mounting an SDM, make sure that the mounting surface is strong enough to support
the weight of the SDM and mount.
• The installation must also withstand very strong shock forces exerted by the vehicle when
it is moving.
Maximum Height: 2' 6"
Maximum Height: 2' 1"
Maximum Height: 1' 8"
8'
10'
12'
12˚
Distance From
Centerline
Horizontal
Plane
Satellite
signals
OM/E-0093-42
