Fujitsu Corporation

Yoshimi Iijima

Kazuhiro Sato

Kenji Takato

Atsuo Serikawa

Mitsutoshi Ayano

Kiyoshi Shibuya

Hiroyoshi Mori

Kenichi Ogawa

Shoji Nojiri

Yasuo Miyazaki

Kiyoshi Kasahara

A call meter signal receiver is provided for a subscriber's private metering system operated by a call meter signal sent from a central office. The receiver is operable both by common mode and normal mode signals. The receiver is small sized and can be installed in a central office trunk of private branch exchanger equipment. The call meter signal receiver is composed of a frequency tuned receiver including two buffer circuits, the first one for receiving the common mode and the second one for receiving the normal mode signal. The first buffer circuit is connected to the input side of a hybrid circuit of the COT, and has a high impedance, while the second buffer circuit, for receiving the normal mode signal, is connected to one of the output terminals of the hybrid circuit, and has a high impedance for voice signals. The outputs of these buffer circuits are fed to the frequency tuned receiver composed of a phase locked loop, of which frequency is tuned to 50 Hz, 12 kHz or 16 kHz by switching an externally attached circuit composed of a capacitor and resistors.

Call meter signal receiver for subscriber's private metering of

In a calling signal transmitting apparatus, a ring trip equipment, including a ring trip detecting circuit for detecting a ring trip signal in response to an off-hook operation of the telephone set during a signal state of an intermittent ringing signal and a loop detecting circuit for detecting a loop signal in response to an off-hook operation of the telephone set during a nonsignal state of the intermittent ringing signal. Also included are a logical OR gate circuit, for providing, as a status signal, a logical sum of the ring trip signal and the loop signal, and a supervising circuit for supervising the status signal. When an incoming call is being received by the telephone set, when the supervising circuit detects an off-hook state in the status signal, the supervising circuit stops the transmission of a ringing signal to the telephone set, and carries out a second supervising operation for supervising the status signal, and, if an on-hook state is detected during the second supervising operation, said supervising circuit again transfers the ringing signal to the telephone set.

Calling signal transmission apparatus

A communications system for transmitting and receiving data and voice signals simultaneously on 2-wire signal lines, which superposes and extracts high frequency modulated data signals using a high frequency transformer which is coupled to the 2-wire signal line. The transformer has two windings which are short-circuited with respect to high frequency components, but which pass low frequency voice signals between the 2-wire signal line and a low frequency hybrid circuit.

Communications system for transmitting and receiving data and voice

A battery feed circuit for a subscriber line includes first and second feed circuit parts, each supplying a constant current to a corresponding subscriber line. The first and second feed circuit parts are provided with at least one of a common mode noise suppressor and a power source noise suppressor. The common mode noise suppressor includes first and second reference voltage output circuits and an intermediate voltage output circuit to produce the voltage between the first and second subscriber lines and superpose the same onto the first and second reference voltages. The power source noise suppressor functions to cancel the power source noise voltage at the output, of the first and second feed circuit parts.

Battery feed circuit for subscriber line

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Kawasaki, Japan

Yoshimi Iijima