Abstract: In order to reduce the signal loss in a telephone line switching and conferencing system there is interposed between each line and the switching matrix a monobus port circuit arranged to convert a transmitted telephone signal into an equivalent current source. An opto-coupled hybrid replaces the port circuit transformer and serves to provide the desired voltage to current conversion. The currents from several monobus circuits are added in a bus resistor before distribution back to the individual monobus circuits as a voltage where the original signal is subtracted from the bus signal. The resultant signal is transmitted to the telephone receiver via the opto-coupled hybrid. When the switching matrix crosspoint resistance is negligible, the component of the bus voltage measured at the current source output which results from current generated from each port circuit is equal and opposite in magnitude to the voltage generated in the port circuit.

Abstract: In order to reduce the signal loss in a telephone line switching and conferencing system there is interposed between each line and the switching matrix a monobus port circuit arranged to convert a transmitted telephone signal into an equivalent current source. The currents from several monobus circuits are added in a bus resistor before distribution back to the individual monobus circuit where the original signal is subtracted from the bus signal. The resultant signal is transmitted to the telephone receiver. When the switching matrix crosspoint resistance is negligible, the component of the bus voltage measured at the current source output which results from current generated from each line is equal and opposite in magnitude to the voltage generated in the line. In any given line these voltages cancel each other, thereby eliminating the feedback signal.

Abstract: In telephone installations it is often necessary to know, without actually physically going off-hook, the status of the line. A solution to this problem is presented by the design of a low drain line status indicator circuit. Advantage is taken of the fact that the idle line voltage available from the switching machine is significantly greater than the busy line voltage. Accordingly, when the line is idle, a pulsating voltage is developed which is used to flash a light source at the station. When the line is busy or on hold, which situation can occur from a telephone station set connected to a remote extension, the line voltage is insufficient to enable the pulsating voltage circuit and, thus, the light source remains dark. In situations where one telephone station set serves two lines, the light sources associated with each line at each station location are arranged to flash in synchronism.