Nortel Networks 553-3001-211 manual Variable gain filters

Overview Page 69 of 894

Variable gain filters

Audio signals received from the analog phone trunk are passed through a low-pass A/D monolithic filter that limits the frequency spread of the input signal to a nominal 200–3400 Hz bandwidth. The audio signal is then applied to the input of the codec. Audio signals coming from the CODEC are passed through a low-pass A/D monolithic filter that integrates the amplitude modulated pulses coming from the CODEC, and then filters and amplifies the result.

On some of the trunk cards, the gain of these filters can be programmed by the system controller. This allows the system to make up for line losses according to the loss plan.

Balancing network

Depending on the card type, the balancing network is capable of providing either a 600 ohm or a 900 ohm (or both) impedance matching network. It also converts the 2-wire transmission path (tip and ring) to a 4-wire transmission path (Rx/ground and Tx/ground). The balancing network is a transformer/ analog (hybrid) circuit combination.

Signaling circuits

Signaling circuits are relays that place outgoing call signaling onto the trunk. Signal detection circuits monitor the incoming call signaling.

Control signals

Control signals and logic are provided when the trunk is going to be connected to special services such as recorded announcement and paging equipment.

Circuit Card Description and Installation