Section 150-319-124
Revision 03
Page 11
6. HDSL LINE VOLTAGE OPTION
6.01
The symmetry of the HDSL line powering
voltage can be set by the S2 switch, located on the
printed circuit board, as shown in Figure 5.
6.02
The factory default setting is unipolar (-). It
sets the HDSL line voltage to 0 V on loop 2 and to
either -130 V (for non-doubler applications) or -200 V
(for doubler applications) on loop 1. This setting
keeps the HDSL cable pair voltage at or below ground
potential, thereby avoiding corrosion problems caused
by cable voltages more positive than ground.
6.03
The bipolar selection sets the HDSL line
voltage to +65 V on loop 2 and -65 V on loop 1, for
non-doubler applications. Doubler applications will
have +100 V on loop 2 and -100 V on loop 1. This
setting reduces the maximum ground referenced
voltage to 100 V, but applies positive voltage to the
cable pairs, which could accelerate corrosion on the
cable pairs.
6.04
The line voltage power supply, used for both
options, is ground referenced, but also ground isolated
by 200 kohms. This ground isolation reduces
problems due to induced noise currents and large
surge voltages, which are ground referenced. It also
reduces ground fault currents, which improves the
product’s safety. The safety issue thus depends
solely on the differential voltage across loop 1 and
loop 2, and is independent of S2’s setting.
Figure 5. HDSL Line Voltage Switch S2
