Abstract: The present key telephone system comprises cordless telephone stations (FIGS. 6 and 7) which communicate over a line-of-sight transmission end link (276 or 277). The system further comprises a central controller (101) for switching communications between the cordless stations and to the message network. The central controller does not provide any station to transmission channel concentration. Concentration occurs in the bidding by a cordless station for access to a channel provided by the line-of-sight transmission end link. A particular number of transmission channels are provided by the line-of-sight end link which are bid for by any practical number of cordless stations. Subsystem controllers (104) are provided in a large cordless key telephone system. The subsystem controller reformats data for transmission between the central controller (101) and a cordless station.

Abstract: A noise detector and data signal receiver for a frequency modulation system has a first phaselock loop circuit (300), responsive to the received signal, for providing a signal indicative of the noise level and a first stage of demodulation of the received signal. A high speed comparator (330) of the first phaselock loop circuit provides a 90 degree phase-shifted signal which exhibits lesser delay and is substantially in phase with the input. Accordingly, the noise detection capability of the phaselock loop circuit (300) is improved. A second phaselock loop (200), also responsive to the received signal, extracts a voice signal from the received signal. A third phaselock loop (400) responsive to the once demodulated output signal of the first phaselock loop (300), extracts a digital data signal from the received signal. Squelch circuits (120, 121), activated at separate particular levels of noise, are responsive to the noise level indicator signal of the first phaselock loop.

Abstract: An off-hook/on-hook status check circuit is adapted to be connected in series with either the tip (2) or the ring lead (3) of a telephone subscriber loop (1) at a location remote or apart from the telephone station set (13). The circuit comprises an opto-emitter subcircuit (7) in series with a capacitor (4). These are connected in parallel with a pulsing contact (K.sub.1) which alternately permits the charging of the capacitor by the telephone central office voltage or its discharge through the opto-emitter subcircuit. As the capacitor may only be charged when the telephone station set is off-hook drawing loop current, the opto-emitter subcircuit provides a predetermined output when the capacitor discharges, identifying the off-hook condition of the telephone station set. No output from the opto-emitter subcircuit during the capacitor discharge interval identifies the on-hook condition of the set.