4 wire Analog Communication Interface

Discussion in 'General Electronics Chat' started by themaccabee, Feb 28, 2012.

  1. themaccabee

    Thread Starter New Member

    Oct 26, 2010

    I’ve a 4 wire telephone leased line interface..2 wires for Tx & 2 wires for Rx.
    Over this link commands are transmitted and received as frequency tones for analog communication.

    I need an isolation transformer to interface my circuitry towards it

    I hope to convert the signal from line side to unbalanced on the board side using a transformer. But I’m not sure how to select the transformer properly.

    The following are some transmitter side parameters

    RL 20dB
    LCL 300-600Hz 40dB
    600-3400Hz 46dB
    Nominal output impedance 600Ohm
    Output level range -30 to +12dBm
    BW 300Hz-4000Hz
    Isolation 1500V

    Can u please help me to select a proper device?

    Also while converting to unbalanced state on the board side, ive seen a circuit with a parallel resistor to ground on the board side in a schematics,
    Can u plz tell me how to design properly the resistor value and if the impedance need to be maintained at the board level tracks as 600Ohms, like in RF PCB s as 50Ohm tracks??

    Also there exists a case where multiple such units are used ..So then there need to be a 0 Ohm point (Tx)and as well as a 10kOhm position (Rx) .can u please advice me what to do in such cases?