Internal telephone conference circuit - has modified connection channels permitting participation of public telephone subscriber to participate

摘要

The circuit arrangement is for connecting member stations of an internal telephone plant to a conference circuit (WN). Public telephone subscribers (Al1 to Al2etc.) may also be connected to the same conference circuit via a two-wire line (M1,M2 etc.) and a transformer-coupled connection (GA) to the conference circuit. No attenuator circuit member is required in the a-b line pair line imaging attenuator and termination circuit (LNA) have to be adjusted to the associated line. The attenuation circuit consists, in all cases, of a vertical T-member made of a resistor and parallel capacitor, with resistors situated symmetrically on both sides on the 'a' and 'b' lines. Capacitive cross links pass from the a-line input to the b-line output, and from the b-line input to the a-line attenuator output.