Furuno FELCOM251, Installation Manual

Page: 63 / 122

4. GROUNDING AND RF PROTECTION
4-10
4.6.2 Grounding the antenna
If the mounting base of the antenna is electrically connected to the hull (or any other
ground potential than the Communication Unit), the antenna must be isolated at its
mounting bolts by means of shoulder bushings and washers – see section 4.9.3. This
is done in order to prevent DC currents flowing in the hull thus causing electrolytic cor-
rosion.
However, a ground connection must be established via one of the mounting bolts us-
ing a separate ground cable. The ground cable must be routed parallel and in close
proximity to the shielded coax cable hence connecting the antenna to the Communi-
cation Unit Grounding kit. A tinned heavy gauge wire (min. 6 mm
2
) can be used for
this purpose – see the figure below.
Alternative grounding for aluminium hulls
4.7 Alternative Grounding for Fibreglass Hulls
4.7.1 Grounding the Communication Unit
The Communication Unit must be grounded with the short antenna cable and optional
grounding kit (S-67-127570). Further, the Communication Unit must be grounded at
its grounding stud in order to ensure a proper grounding if the short antenna cable is
disconnected.
The ground connection must be established at a dedicated RF ground (either capac-
itive or electrical coupled). Bear in mind that the antenna ground connection is to be
made at the
same electrical ground potential as the Communication Unit (see
section 4.7.2).
Heavy Gauge
Wire
RF Ground
(Capacitive OR seperate ground plate)
- +
Communication Unit
Grounding Kit
Communication
Unit
Antenna
Unit
Antenna
Unit