Abstract: In a telephone line feeding arrangement, the line current is monitored by a multi-resistor network (R.sub.p R.sub.s) and the output of the network applied to the inputs of an operational amplifier (A3). The output of this amplifier, which is a voltage whose value depends on the line current, is compared by a comparator (A4) with a reference voltage (V.sub.R) to produce a control voltage for a variable voltage (VVS), the output of which provides line feeding voltage.In an alternative, the monitoring is effected by connecting the two line wires each via a resistor to one of the inputs of an operational amplifier (A6) whose output is a voltage dependent on line voltage. This voltage is applied to an input of another operational amplifier (A7) where it is in effect added to a reference voltage (V.sub.R). The output of this amplifier (A7) is used to control the variable voltage source (VVS), which in turn controls a constant current source (CCS) whose output provides line current.

Abstract: The invention relates to a fire alarm system in which the fire alarm is located in an enclosure which must be entered by the operator of the fire alarm, and the door to the enclosure, or opening through which the operator passes, must be closed in order to initiate the actuation of the fire alarm. The fire alarm within the enclosure has a fire alarm switch located to be covered by a door or plate which must be moved in order to have access to the fire alarm switch. Circuits are provided which upon the closing of the door cause a circuit to be energized while the movement of the cover for the alarm switch allows the alarm switch lever to be moved only if the operator is located in the enclosure containing the fire alarm. The alarm switch actuates a door lock and a timing device which will hold the operator within the enclosure for a given length of time sufficient for the firemen to reach the scene of the alarm.

Abstract: An electronic exchange of the time division system type or the space division system type, employing electronic contacts, in which a U-junctor is connected to the switching network of the electronic exchange. The switching network program for controlling the connection of the switching network regards the U-junctor as a combination of an outgoing and an incoming trunk. The connection between the trunks, between subscribers or between each subscriber and each trunk in a special calling service is controlled by using the U-junctor and the switching network.

Abstract: A combination directional gyro and navigation radio indicator instrument for use in aircraft which provides a display of compass card, selected course pointer, course deviation indicator, to-from indicator, and glide slope indicator in a unique presentation. The compass card is directly driven by the directional gyro, and the selected course pointer normally rotates with the compass card when it rotates, but can be de-clutched for selection of a new course. The selected course signal is obtained by attenuating, amplifying, and phase shifting the reference signal from a navigation radio such that it can be sent to the rotor of a control transformer which is geared to the compass card. The resulting stator signal is then amplified and sent to the rotor of a differential resolver which is geared to the course selector pointer.

Abstract: A system for the transmission of digital data in packets comprising transmission and reception means, wherein:the transmission means are able to form single words taken in a group of words each having 2n bits and constituted by a word M of n bits between which are inserted the n bits of the complement word M, the bits of M being displaced relative to those of M by a number p of ranks, the choice of p defining a single word of the group;in the reception means there is only one single word detector and it functions with n bits, said detector being able to detect the displaced appearances of p ranks of words M and M on each bit sequence of even rank and uneven rank.

Abstract: A method and apparatus for measuring signal to noise ratio in a time division multiple access (TDMA) communications system which does not require that normal communications be interrupted. The signal to noise ratio measurement is performed on the unmodulated carrier which typically occurs in the preamble of each information burst in the TDMA format. In order to perform the measurements on the carrier of the same burst in each frame, the carrier and noise powers are sampled at a predetermined time with respect to specified information which occurs at the same time in each frame, normally the frame reference burst. After being converted to the receiver intermediate frequency, the unmodulated carrier is fed to both a narrow band pass filter having a pass band at the intermediate frequency and a narrow band stop filter having a stop band at the intermediate frequency. The ratio of the band pass filter output to the band stop filter output is the signal to noise ratio within a very small error.

Abstract: Speech signals from a plurality of channels are interpolated in a TASI system for transmission via a lesser plurality of transmission facilities, such as telephone tie-lines which carry analog voice frequency signals. Recurrently, the level of noise received via each facility is measured at a receiver of the system while the facility is idle. An average of the monitored noise levels for all facilities, which is recurrently updated, is used to control the level of a noise signal which is supplied by the receiver to each off-hook channel for which speech signals are not being received via the facilities.

Abstract: A delay correction circuit is described for use with an elastic store in a PCM time division multiplexed system. The relative position of the read and write addresses supplied to the elastic store are monitored. In the event that either the read or write addresses are overtaking the other and are within a predetermined range of addresses, either the read or write address source will be initialized at a predetermined time such that the read and write addresses have new relative position.

Abstract: In a contactless keyboard including for each key a transformer with a core displaceable by the key operation and including a compensation transformer common to all key the compensation transformer is so designed that with an unactuated key the signal component of the compensation transformer in the signal applied to the evaluation circuit exceeds the component of the key transformer, whereas with an actuated key the signal component of the key transformer predominates. Therefrom results a phase change of the signal applied to the evaluation circuit with the actuation of a key. The evaluation circuit compares the phase of the key output signal with that of a reference signal. For increasing the immunity from disturbance the evaluation circuit delivers an output signal (key operated or key nonoperated) only when several successive comparison operations give the same result.

Abstract: The consequences of the loss of a packet are attenuated in a digital data communication apparatus using packet switching by structuring the digital data as multibit words into frames having a fixed length l and assembling the frames into packets all having the same predetermined length L=kl, where k is a predetermined integer. Continuity index words incremented by one each time a new frame or packet is assembled may be located into the frame locking word or the packet prefix. Then the number of packets which are lost may be determined at the receiver location by monitoring the successively received index words. When the digital data represent successive samples which are correlated, for instance when such samples represent a sound, substitution data may be generated at the receiver location and used in place of the missing data.

Abstract: Incoming data words organized in a succession of multi-channel frames, arriving at a receiving section of a PCM station, are fed in parallel therewith to a correlation circuit forming part of a synchronizing unit which includes a timer stepped by line-clock pulses extracted from the incoming bit stream. The correlation circuit includes a decoder which recognizes predetermined bits or bit combinations in alignment words A and B respectively appearing at the beginning of alternate frames. Recurrent noncoincidences of either of these alignment words with a corresponding marking pulse emitted by the timer, in a time slot designating the No. 0 channel of a frame, causes a readjustment of the timer and thus a shifting of clock signals emitted thereby to the receiving section. The synchronizing unit, embodied in an integrated-circuit chip, further includes a malfunction detector responsive to signals emitted by the timer and by the decoder of the correlation circuit.

Abstract: A track circuit is disclosed and includes rails which are fed from a main signal transmitter and which rails, at an information point a required distance from the transmitter, are shunted by a cross impedance, with which impedance, with respect to the track of the main signal, an additional transmitter of an auxiliary signal and a main receiver for receiving signals from the main and additional transmitter are serially connected. A signal indicating a free track is obtained if the main receiver is energized.

Abstract: An automatic self-test apparatus for use in a digital multiplexed communication system and self-testing idle circuitry coupled to idle telephone lines. The apparatus utilizes a tone generator which generates digital words describing an analog test signal and a detector which detects digital data on the internal data bus which describes this self-test analog signal. The data from the tone generator is coupled to the circuitry connected to the idle line through a time division multiplexer under the control of a controller consisting of a programmed microprocessor. The microprocessor controls when the transfer is made and to which telephone line it is directed. This control is accomplished by writing a control word to a multiplexer naming the source and destination for the transfer and the time slot in which it is to occur. When the circuitry connected to the idle line functions properly, the controller proceeds to the next idle line. If a malfunction is detected, the controller sets an alarm.

Abstract: A supervisory channel is provided on a digital transmission system by frequency modulation of the data signal transmitted along a transmission link which includes repeaters. The frequency modulation can be carried out using an elastic store. Each repeater includes means for demodulating the frequency modulation so that each repeater can be addressed and interrogated. Each repeater can also phase modulate the data signals on the return link to a terminal station so that signals indicative of an interrogated condition can be transmitted to the terminal station.

Abstract: In an SS (spread spectrum) modem, a high-pass filter (81) for rejecting a low frequency component including an information signal received by demodulation, produces an SS signal component modified by a PN (pseudo noise) code sequence used for the demodulation. A multiplier (82) substantially regenerates the SS signal component. Band division may be resorted to, in which case an input filter (161) selects a partial band SS signal for the demodulation. A transit filter (164) rejects the partial band SS signal. An SS signal is sent to a destination modem through one of output filters (162) selected for the destination modem. Each generator (67, 71) may generate a PN code sequence given by a product of PN codes, one having a frame period equal to an integral multiple (unity allowed) of the PN clock period of another. Each partial band may be about 1/5 of the entire frequency band of the PN code sequence. A center portion of the band may be used in transmitting a narrow-band synchronizing signal.

Abstract: A wireless signaling between one or more remote locations and a central location includes a transmitter at each remote location and switches for providing signals indicating status information on each remote location. A logic circuit coupled to the switches and to the transmitter provide signals effecting transmission of a signal modulated to uniquely identify the remote location and the status represented by the switches. A receiver at the central location is coupled to a second logic circuit for decoding the signals received from the transmitter and is coupled to indicators for providing an indication of the status at the first location.

Abstract: In a data transmission system with such a construction that a plurality of terminal units are connected to a first and a second loop transmission line for transmitting messages in a first direction and in a second direction which is opposite to said first direction, respectively, through a pair of transmission control units (the one unit being connected to said first loop transmission line with the other unit being connected to said second loop transmission line), each transmission control unit sends a check message sequentially in order to check the state of a minor loop which connects two adjacent pairs of transmission control units. This check message has a data field, in which an initial value is set at the sending time. The value of this data field is incremented by one in each transmission control unit through which the message passes to make a round through the minor loop.

Abstract: A small capacity digital PBX-key system which uses a single processor to control the system. Since only a single processor is employed, the system is interrupt controlled. In the system, there is a codec per line, the codecs each having sufficient programmability to eliminate the need for time slot interchangers. To provide as many as 64 (or more) channels usable for speech, tones and conferencing, two (or more) parallel, 32 channel busses are used as the group bus. The stations and trunks (ports) of the system have access to both busses through the codecs. Information is routed to one or another bus through the transmission of bus control bits from the processor.

Abstract: A loop controller transmits data to and receives data from a plurality of I/O ports on a TDM serial loop by generating a plurality of frames which include a frame control field followed by a plurality of dedicated time slot fields. Each time slot field includes an inbound data control bit or bits followed by a data field followed by an outbound data control bit or bits. The I/O port inputs and outputs data in its dedicated data field as dictated by the respective data control bit. The loop controller and I/O ports monitor the data control bit to request data, indicate insertion of data, indicate receipt of the data and acknowledge the receipt indication to achieve a complete handshake. During an initialization frame, the I/O ports set themselves into primary and secondary data modes based on sensing a prior I/O port with the same dedicated time slot.

Abstract: A displacement converting circuit arrangement comprising first and second capacitors in the form of a paired structure, at least one of the capacitors having a capacitance which is varied in response to a mechanical displacement. Means are provided for deriving first and second currents respectively proportional to the capacitances of the first and second capacitors, means for maintaining at least one of the DC currents corresponding to at least one capacitor having a variable capacitance at a fixed amount, and means for producing an output current corresponding to the difference between the DC currents, so that the output current indicates the amount of the mechanical displacement. Operation stability is improved by the simplified circuit arrangement, with consequent reduction in error and circuit failure. The movable electrode for varying the capacitance can withstand a heavy load.