Nortel Networks 553-3001-211 manual Carrier grounding, Impedance matching, Receiver functions

NTAK79 2.0 Mb PRI card Page 743 of 894

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 240.

Table 240

Impedance matching switch selection

Cable	On	Off
75 ohms	S2	S1
120 ohms	S1	S2

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 241.

Table 241

Carrier shield grounding switch settings

Switch	Carrier Pair	On	Off
S4-1	Rx shield	Open	GND
S4-2	Tx shield	Open	GND

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

Circuit Card Description and Installation