NorthStar 941X Reference Manual page 117

grounding
Rev. D
is molded into the lower portion, or base, of the ACU body into which the
upper half is secured (see Figure 9 on page 110). The bottom of the base
is threaded (1"–14) to mount onto the antenna mast or onto a standard
deck mount. A gasket and rubber O-ring provide weathertight sealing at
the ACU base.
The ACU connects to the receiver by a single 25-foot length of RG-58U
coaxial cable which carries signals to the beacon receiver and DC power
to the ACU amplifier. The cable passes up through the hollow ACU base
and connects to the PL-259 (UHF) connector at the bottom of the ACU
(see Figure 10 on page 111 for UHF connector preparation). Note: This
connection must be made before the ACU is screwed into its base.
The grounding system is an equal partner with the antenna in producing
quality signals for the 941X DGPS beacon receiver. Essentially, the
ground system provides a secure connection to a large electrical mass;
ideally, the earth itself. On a vessel, this means establishing electrical
contact with the sea. On a steel vessel, a good connection to the hull or
steel pilothouse is sufficient. Wood or fiberglass vessels require a metal
ground plate. If the metal ground plate is impractical, the engine block or
the negative (–) battery terminal can sometimes be used, but only as a
second choice.
Lack of proper grounding can adversely affect beacon signal strength, as
well as SNRs, and is the most common source of problems with beacon
antenna installations. The 8410 ACU has a separate black ground wire
inside the coupler base. This wire is the AC signal ground connection
from the antenna input circuit. The purpose of bringing it out is to make
available a separate signal ground path.
Other electrical equipment onboard can cause large amounts of electrical
noise, even at points that appear well-grounded. Try several ground
points (ground plate, vessel ground, engine block, etc.) to determine
which works best under different conditions.
9 — Installation and Interfacing 9 — Installation and Interfacing
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