Nortel Networks Circuit Card - Manual (Page 755)

NTAK79 2.0 Mb PRI card Page 755 of 906
Circuit Card Description and Installation
Impedance matching
The line interface provides for the use of either 75 ohms coaxial or 120 ohms
twisted pair cable. The impedance is selected by a switch, as shown in
Table 245.
Note: The ON position for all the switches is towards 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
The NTAK79 card provides the capability of selectively grounding the shield
of the Tx and/or Rx pairs of the carrier. Closing (down) the on-board switch
applies FGND to the appropriate carrier cable shield. The switch settings are
shown in Table 246.
Receiver functions
The receiver extracts data and clock from an AMI (Alternate Mark Inversion)
coded signal and outputs clock and synchronized data. The receiver is
sensitive to signals over the entire range of cable lengths and requires no
equalization. The clock and data recovery meets or exceeds the jitter
specifications of the CCITT recommendation G.823, and the jitter attenuation
Table 245
Impedance matching switch selection
Cable On Off
75 ohms S2 S1
120 ohms S1 S2
Table 246
Carrier shield grounding switch settings
Switch Carrier Pair On Off
S4-1 Rx shield Open GND
S4-2 Tx shield Open GND