Installation Manual

89-041 Section 4 Issue 5 S4-5
Whether termination at the terminal board is required depends on how the other units are
connected, and whether any of these other units provides termination for the signal line. The
following sketch shows the principle:
There is only one talker per twisted pair; there can be several listeners. The requirement is that
terminations must be provided by the devices at the ends of the line, regardless of whether they
are listeners or the talker, and that no other device should provide a termination.
A terminal is provided for the common connection at each port on the screw terminal board;
particular care should be taken to ensure that the cable screen is connected to ground only at
the talker.
Do not connect the cable shield to ship’s ground at both ends of the cable as this may cause
ground loops and interference to the signals.
Note: For clarity, the sketch shows the devices connected to the twisted pair by spurs; in
practice, the twisted pair is looped through each device in turn.
It is good practice to use screened cables in all ship cable installations. In the transponder unit
the screen from some cable entries should be connected to ground at the entry to the
transponder unit, as shown in the table. The technique of connecting the screen is illustrated
below.
Switch Lines terminated by resistor Connect screen
at transponder
S2 (brown) DISP Display (VDU) port YES
S2 (red) LR Long Range port PREFERRED
S4 AUX Auxiliary or Pilot port PREFERRED
S5 (brown) MAIN Main port PREFERRED
S5 (red) RTCM RTCM port for differential correction PREFERRED
S6 SEN 1 Sensor 1 port NO
S7 SEN 2 Sensor 2 port NO
S8 SEN 3 Sensor 3 port NO
PREFERRED means that the screen may be connected either at the remote device or at the
transponder; if no other considerations apply, connection at the transponder is recommended.