Nortel Circuit Card Installation Manual page 755

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.
Table 245
Impedance matching switch selection
75 ohms
120 ohms
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.
Table 246
Carrier shield grounding switch settings
Switch
S4-1
S4-2
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
Cable
Carrier Pair
Rx shield
Tx shield
NTAK79 2.0 Mb PRI card
On
S2
S1
On
Open
Open
Circuit Card Description and Installation
Page 755 of 906
Off
S1
S2
Off
GND
GND