Abstract: An emergency telephone system has a dual mode, hybrid emergency telephone station connected with a central station through both a digital ethernet connection for digital VOIP communication and through a wire line for analog communication. Circuitry at the dual mode emergency station connects a user terminal with the digital ethernet connection and the wire line. A processor forming a part of the circuitry directs communication through the ethernet connection if operative and through the analog wire connection if the ethernet connection is inoperative.

Abstract: A muting circuit for a transconductance amplifier has a switch connected across the signal load of the amplifier to short circuit the output.

Abstract: A power supply for an operational transconductance amplifier has positive and negative terminals to which the positive and negative power terminals of the amplifier are connected. A stable reference potential is established with respect to one of the power supply terminals. The signal input and output circuits connected with the amplifier are referred to the stable reference potential and the amplifier is operated to maintain the output signal at a level such that the power supply noise does not affect the output signal.

Abstract: A two channel intercommunication system has a high degree of noise immunity. The gain of each channel is controlled by a gain control loop processing circuit. The signal condition in one channel turns off the other channel. Multiple active rectifier-filter circuits discriminte between speech and noise and provide timing of control signals.