Nortel Circuit Card Installation Manual page 781

Impedance matching (Switch SW2)
The line interface provides for the use of either 75 ohms coaxial or 120 ohms
twisted pair cable. The impedance is selected by SW2, as shown in Table 251.
Table 251
Impedance matching switch settings
Note: The ON position for all the switches is toward the bottom of the
card. This is indicated by a white dot printed on the board next to the
bottom left corner of each individual switch.
Carrier grounding
NTBK50 enables the shield of the Tx and/or Rx pairs of the carrier to be
selectively grounded. Closing (down position) the on-board switch applies
FGND to the appropriate carrier cable shield. The switch settings are shown
in Table 252.
Table 252
Carrier Shield grounding switch settings
Switch
SW 4 – 1
SW 4 – 2
NTBK50 2.0 Mb PRI card
Cable Type
75 ohms
120 ohms
Down (On)
Rx – FGND
Tx – FGND
SW 2-1
Down (On)
Up (Off)
Circuit Card Description and Installation
Page 781 of 906
Up (Off)
Rx – OPEN
Tx – OPEN