Bell Telephone Laboratories

Other

At&t Bell Laboratories

Dennis Bryan James

Douglas C Smith

Chao Kai Liu

Bryan Scott Moffitt

John Francis O'Neill

Alexander Feiner

James R McEowen

Robert M Smith

A one-piece, hand-held slat ripper for cutting slat, such as vinyl fencing slat, in lengths of uniform width, which includes an enclosed channel of uniform rectangular cross-sectional area housing a blade safely disposed within the channel.

Slat ripper

A must system for use in conjunction with a normally air cooled air conditioner condenser. The mist system provides cooling water to the coils and fins of the condenser to improve efficiency. Misting is normally off but comes on in response to pressure in the high pressure supply line from the condenser rising above a pre-set head pressure level.

Air conditioner mist applicator

High density time division busses suffer from many problems, one of which is that impedance discontinuities cause signal reflections to occur along the bus. These reflections, in turn, affect the settling time and noise margins of the bus and thus reduce the time 'window' in which valid signals may be received. There is disclosed a transmission bus structure which allows for bidirectional, multi-port operation by using current drivers instead of the traditional voltage drivers for placing data signals on the bus. The transmission bus is designed in a manner which allows transmission and reception from a single clock on the same clock edge thereby substantially increasing the time allowed for transmission response and also simplifying the clock distribution requirements.

Distributed time division multiplexing bus

The disclosed signal limiting circuit is bridged on to a bidirectional communication path (T, R) and functions to selectively attenuate excessive signals (2V.sub.A) being transmitted in a predetermined direction on the bidirectional communication path. This is accomplished by a signal discriminator circuit (100) which separates the excessive signal (2V.sub.A) from the plurality of signals appearing on the communication path (T, R). The signal discriminator circuit (100) also inverts the isolated excessive signal, passes it through an attenuator (102) to a signal injection circuit (103) which injects a controlled amount of the 180 degrees out-of-phase isolated excessive signal back on the communication path (T, R) to cancel out a portion of the excessive signal, thereby providing selective attenuation of the excessive signal.

Signal limiting circuit

In order to reduce the signal loss in a telephone line switching and conferencing system there is interposed between each line and the switching matrix a monobus port circuit arranged to convert a transmitted telephone signal into an equivalent current source. An opto-coupled hybrid replaces the port circuit transformer and serves to provide the desired voltage to current conversion. The currents from several monobus circuits are added in a bus resistor before distribution back to the individual monobus circuits as a voltage where the original signal is subtracted from the bus signal. The resultant signal is transmitted to the telephone receiver via the opto-coupled hybrid. When the switching matrix crosspoint resistance is negligible, the component of the bus voltage measured at the current source output which results from current generated from each port circuit is equal and opposite in magnitude to the voltage generated in the port circuit. In any given line these voltages cancel each other, thereby eliminating the feedback signal.

Monobus interface circuit using opto-coupled hybrids

In order to reduce the signal loss in a telephone line switching and conferencing system there is interposed between each line and the switching matrix a monobus port circuit arranged to convert a transmitted telephone signal into an equivalent current source. The currents from several monobus circuits are added in a bus resistor before distribution back to the individual monobus circuit where the original signal is subtracted from the bus signal. The resultant signal is transmitted to the telephone receiver. When the switching matrix crosspoint resistance is negligible, the component of the bus voltage measured at the current source output which results from current generated from each line is equal and opposite in magnitude to the voltage generated in the line. In any given line these voltages cancel each other, thereby eliminating the feedback signal. In situations where it is desired to use crosspoints having an unknown resistance, the voltage returned from the monobus does not exactly match the locally generated voltage because of the voltage drop across the crosspoint and thus a feedback signal of unknown magnitude is applied to the telephone line. This unknown deviation of signal gives rise to gain contrast from one connection to the next and modifies the return loss in an unpredictable fashion. This problem has been solved by separating the connections of the monobus into transmit and receive paths and connecting each path to the bus through a separate crosspoint.

Monobus variable resistance transmission circuit

In telephone installations it is often necessary to know, without actually physically going off-hook, the status of the line. A solution to this problem is presented by the design of a low drain line status indicator circuit. Advantage is taken of the fact that the idle line voltage available from the switching machine is significantly greater than the busy line voltage. Accordingly, when the line is idle, a pulsating voltage is developed which is used to flash a light source at the station. When the line is busy or on hold, which situation can occur from a telephone station set connected to a remote extension, the line voltage is insufficient to enable the pulsating voltage circuit and, thus, the light source remains dark. In situations where one telephone station set serves two lines, the light sources associated with each line at each station location are arranged to flash in synchronism.

Growing community of inventors

Rumson, NJ, United States of America

Dennis Bryan James