19
Nera F77
Continuing the Saturn tradition
Grounding considerations
A successful installation of a maritime satellite terminal must take
into account the noisy environment in which the equipment shall
operate.
Electrical noise
The electrical environment on board a ship is usually quite noisy.
Powerful electrical installations cause voltage variations and
transients, as well as low and high frequency noise. Radio and
radar equipment radiate radio frequency signals which frequently
impregnate cables on board with unwanted interference.
Ground plane
Most ships have a steel hull. One should think that the steel
construction of the ship would constitute a good ground plane.
This is often not quite true. Rust, other forms of corrosion, paint
and grease, often prevent a good ground connection. A conse-
quence of this is that high energy power distribution on board a
ship can cause significant ground potential differences.
Antenna unit
Adequate grounding of the Antenna Unit depends on the
fastening bolts making good contact with the top flange of
the mast. This is obtained by removing paint and using
enclosed toothed washers and nuts.
Antenna cable
The antenna coaxial cable normally has a solid or meshed metal
screen which must be terminated to ground both at the antenna
pedestal and at the MCU. The length of the cable can often be
more than 40 metres. If the ground potential level at the two
points differ, the current passing through the screen of the co-
axial cable can be quite strong. The antenna cable screen consti-
tutes a heavy gauge wire, which is capable of conducting large
amounts of current.
Below Deck Equipment
The MCU must be provided with a good electrical connection to
the ship’s hull for grounding. This is obtained by using
copper
foil
. (
See Installation: "
Location and grounding of units
".)
Length of copper foil/10 cm should not exceed 300 cm. The foil
should be connected to ship's hull (deck or roof) by hard-solder-
ing (or screws) to steel.
Mains power/ground
Mains ground is secured to the common grounding point through
the external supply. It is therefore important to use the same
mains branch for additional equipment connected to the MCU
(Fax, PC w/printer etc.).
Summary of Contents for F77
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