NorthStar 951X Installation Manual - page 35
SECTION TWO - Installing the unit
951/952 INSTALLATION MANUAL Revision B
Page 25
RF grounding
The grounding system is an equal partner with the antenna in producing
quality differential beacon signals for the 951/952 differential receiver.
Essentially, the ground system provides a secure connection to a large
electrical mass; ideally, the earth itself. On a vessel, this means establish-
ing electrical contact with “seawater” ground. On a steel vessel, a good
connection to the hull or steel pilothouse is sufficient. Wood or fiberglass
vessels require a metal ground plate or a thru-hull fitting. If the metal
ground plate is impractical, the engine block or the negative (–) battery
terminal can sometimes be used, but only as a last choice due to stray
electrical noise that may be present at these locations.
Lack of proper grounding can adversely affect differential signal strength,
as well as SNRs, and is the most common source of problems with differ-
ential antenna installations. The same grounding techniques that have
worked well for loran systems will work equally well for differential
antenna systems. 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. Use #16 AWG minimum for grounding. If
possible, use a grounding “strap” that is designed for this purpose.
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, and so on) to deter-
mine which works best under different conditions.
Differential GPS antenna cable connectors
Both ends of the differential beacon receiver antenna cable terminate in
UHF connectors. To prepare UHF connectors, follow the assembly
instructions in Figure 18. For best results, coat these connectors with sili-
cone dielectric grease (DC 4 or equivalent) to protect the connector junc-
tion against water intrusion and surface corrosion of the contacts. In
addition, protect the connector area, including the shield-to-connector
junction and jacket-to-crimp ferrule area, with liquid electrical tape (Star-
bright Liquid Tape comes in color-coordinating black or white) or
self-vulcanizing electrical tape (Tommy Tape).
WARNING!
Whenever any antenna is disconnected from on-board equip-
ment, be sure to ground the antenna shield in order to dis-
charge extremely large static voltages that can quickly build up
on an ungrounded antenna system. These voltages are haz-
ardous to personnel and equipment!