Abstract: In a cordless extension telephone system in which a base station is connected to telephone lines and communicates with a remote station by radio transmission, the base station in response to the presence of a ring signal on the telephone lines repeatedly transmits an eleven bit code at a predetermined bit rate. The remote station upon receiving the eleven bit code at least three times in succession generates an audio signal to indicate the presence of a incoming call. The user at the remote station may actuate a control to an "on" position or an "off" position. The remote station responds to the actuation of the control and will repeatedly transmit the eleven bit code plus one additional bit having a state indicating whether the control is actuated to the "on" state or the "off" state. The base station in response to receiving the eleven bit code at least three times in succession will enble or disable an isolation circuit in accordance with the twelfth bit of the code.

Abstract: A circuit for interfacing a telephone system, such as a cordless telephone, to telephone lines by the use of opto-couplers, arranged to establish a telephone line loop upon detecting a ringing signal on the telephone lines. Preferably, three opto-couplers are used in varying combinations to provide a standby condition, ringing detection, ringing detection shut-off, telephone line loop connection, incoming audio, and outgoing audio functions. Such a circuit eliminates the use of transformers and relays, while meeting regulations.

Abstract: A circuit for providing a constant current to an output stage of a cordless telephone transmitter using AC power lines as a transmission medium to maintain the RF component on the AC lines to within regulated limits. The RF component is sensed to provide a control signal to a voltage-responsive capacitor in a tuned circuit connected to a tuned coupling transformer between a modulating circuit and the transmitter output amplifier. When the RF component exceeds the current limit of 90 mA, the coupling transformer is detuned to maintain the RF current in the power lines to within the regulated limits.