Abstract: A portable, lightweight, self-contained stethoscope includes:(a) an enclosure containing a speaker, and having an acoustic wave outlet port connectible to stethoscope flexible tubing,(b) a housing,(c) a transducer carried by the housing, the transducer including a microphone located to be placed in proximity to a patient's body,(d) circuitry in the housing and having an input terminal coupled with the transducer, said circuitry including amplifier means and filter means, and a battery power supply coupled with said circuitry, said circuitry having a first output terminal, and(e) flexible connection means coupling said first output terminal with said speaker.

Abstract: 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.

Abstract: In a telephone installation in which more than one telephone terminal is connected to one pair of conductors--Tip and Ring--a line status apparatus is provided for each telephone terminal, the apparatus sensing a change in line characteristics resulting from an "off-hook" condition at any telephone and producing an output which is used to provide an indication. Little or no current is drawn from the telephone lines. Typical examples are sensing variations in AC characteristics, as resulting from voice transmission, ringing tones and the like; sensing DC variations, such as voltage drop when a telephone is "off-hook". Indication is generally visual.

Abstract: In a digital carrier-concentration system, utilizing time slot assignment, comprises a delta modulator operable to convert analog signals into a digital binary bit stream, the modulator being responsive to the bit stream to decode a coincident pulse whenever a predetermined number of "ones" or "zeros" occur in the bit stream, a voice detect circuit responsive to the coincident pulse to provide a voice detect output, and a control assigns the stream a time slot in a high bit rate data channel in response to detection of the voice detect output, after a predetermined interval.

Abstract: A base station encoder is connected to a decoder terminal and paging transmitter by means of a single voice-pair telephone line link. Automatic operations reduce operator fatigue and operating costs. Digital, tone-keyed gain controls automatically compensate for line losses. All dialing, including long distance and overseas calls, and station identification are done automatically.

Abstract: A radio control system having a radio-controlled model toy on which a d-c power supply, a receiver and two electric motors are mounted, and a transmitter for maneuvering the radio-controlled model toy, and characterized in that the transmitter is constructed so that a control pulse signal having a pulse level representing signal "1" and a pulse level representing signal "0" is transmitted and the duration of the signal "1" pulses is increased or decreased, and that the receiver is constructed so that driving current is supplied to a motor during the signal "1" pulse duration and to another motor during the signal "0" pulse duration.

Abstract: A key telephone system for a predetermined number of outside lines comprises only one control lead shared per outside line by cables connected between a key service unit and key telephone sets, respectively. Each telephone set has manually operable keys for supplying a higher voltage to a relevant control lead while an outside line is selected for an answer or a reanswer to a call present thereon and substituting a lower voltage for the higher voltage when it is desired to hold an answered call.

Abstract: The reverberation system loudspeaker is fed at one terminal by the direct signal and at the opposite terminal by the delayed signal such that the loudspeaker impedance forms part of the feedback path.

Abstract: A push button to rotary dial converter system for converting push button telephones to provide rotary dial type pulsed outputs. The system provided is universal and can be used with almost any subscriber set that is made to provide push button signals to the telephone system and is especially useful when the telephone system involved is not equipped to receive variable frequency dialing signals. Responsive to the operation of the selected push buttons, pulses are transmitted through the line. The system is unique, among other ways, in that the connection to the network is electronically opened during out pulsing and a parallel power supply arrangement is employed; and it is applicable even when only one pair of hook switche contacts are available, and one side of the pair of hook switch contacts are tied together.

Abstract: An adaptive speech signal detector for use in a 4-wire telephone channel performs an adaptive threshold value setting operation depending on the channel noise level on a transmitter-side channel to detect a speech signal present at the transmitter. The adaptive operation of the speed signal detector is inhibited, however, if the signal level at the related receiver-side channel becomes higher than a preset value. This permits the use of the adaptive speech signal detector with DSI (digital speech interpolation) systems without malfunction due to the operation of an echo suppressor.

Abstract: A circuit which connects a ringing voltage generator to a telephone subscriber loop without allowing harmful, electrical transient discharges to develop. Relay contacts are used to switch current limiting resistors into the loop circuit and ringing voltage generator circuit to limit transients during transfer of the ringing voltage generator to or from the subscriber loop circuit. These current limiting resistors are then switched out of the loop when the transients have dissipated.

Abstract: In an FM stereo demodulator, a detector circuit for detecting a low supply voltage is used. The detection level of this detector circuit is made substantially equal to a supply voltage value at the time when the oscillation frequency of an oscillator circuit for reproducing a subcarrier signal begins to change. The stereo reproduction of the demodulator is compulsorily switched to monaural reproduction by an output from the detector circuit. As a result, the generation of an abnormal sound which is attributed to the beat between the reproduced subcarrier signal having fluctuated and a subcarrier signal component of a received broadcast signal is prevented.

Abstract: A compact portable lectern device having a voice amplifier contained therein which may be easily placed upon a tabletop to provide a speaker's lectern and public address system. The device includes a cabinet case having a hinged panel which when swung open from the cabinet, forms the sloping shelf of the lectern. The hinged panel is provided with a pivotally mounted lever arm support member having its fulcrum laterally displaced and provides significant stability to the lectern shelf without the need of mechanical locks or fasteners. The device is additionally provided with a detachable microphone which may be conveniently stored with the cabinet during transport.

Abstract: A system is disclosed for automatically reducing reverberation in typical voice telecommunications systems. This system uses center clipping levels adaptive to the level of reverberation input speech. In one configuration, the voiceband is divided into two sub-bands and center clipping occurs only for the lower band; costs are reduced with surprisingly little transmission quality sacrifice. Clipping-level holdover circuitry with exponential decay appears to work well for a large variety of reverberant enclosures.

Abstract: An improved frequency sensitive circuit capable of adjusting one or more of its parameters in order to shunt an adjustable amount of electrical signal to a current sink, thereby controlling the amplitude of the signal. The frequency sensitive circuit is connected to the wiper of a potentiometer that is placed across the inputs of a difference amplifier in order to control the peak value of the cut or boost in the signal. The frequency sensitive circuit includes a shunt impedance connected between the wiper of the potentiometer and the current sink. A resonant circuit is connected to the impedance and is tuned to an adjustable resonant frequency. A compensation circuit, such as a difference amplifier referenced to the wiper, couples the output of the resonant circuit to the shunt impedance so that the impedance of the frequency sensitive circuit approaches infinity as the frequency of the electrical signal is displaced from the resonant frequency.

Abstract: This hands-free telephone prevents acoustic feedback between its speaker and microphone by attenuating either the transmission or receive path under the control of a corresponding pair of counters (computers), each counter sensing the signal divided and digitized from its corresponding path. An increase in counted pulses indicates feedback and causes a counter to more quickly reach a predetermined counter state (count), to trigger attenuation (damping) before it can be reset (restored) to zero by the other counter.

Abstract: Disclosed is an echo suppressor circuit which provides a variable loss in a speaker's transmit path, which loss is a function of the relative speaker volumes. The loss provided in the path of a particular speaker is relative to the volume of the speech emanating from each speaker. In one embodiment, the amplitude of the incoming signal is reduced by an amount which is a function of the ratio of the amplitude of the incoming signal to the amplitude of the outgoing signal. Because loss is introduced into a distant speaker's transmit path rather than into his return path, it is possible for a near speaker to break into a conversation before the distant speaker has concluded. Further, since the loss provided is a function of the relative volumes of both speakers with respect to one another, the total loss introduced into the system is minimized.

Abstract: To facilitate the supervision of long-distance telephone traffic over an extended area, output signals from call monitors associated with a number of trunk lines are fed to respective detectors working into a common preprocessor in which certain parameters of toll calls carried by each of these trunk lines, such as number and length of engagements, number and length of conversations and number of metering pulses, are registered in real time with the aid of respective counters for subsequent transfer to a final processor. The contents of each counter are read out to a buffer memory, within the preprocessor, upon the termination of the respective call or at any time in response to an external command. The preprocessor may be duplicated in order to minimize the effect of malfunctions, with inhibition of the loading and unloading of the counters of either unit until a confirmation signal is received from the other unit or a certain number of operating cycles have elapsed.

Abstract: A demodulation circuit for an FM stereo receiver is constructed to invert the FM stereo composite signal by an inverting amplifier and then to supply the inverted signal to a switching circuit for producing demodulated left and right signals. The composite signal is applied to a phase-locked loop circuit for applying a 38 kHz switching signal to the switching circuit. A 19 kHz signal produced by the phase-locked loop circuit is converted into a sine wave signal by a waveform converting circuit. The sine wave signal is converted into a direct current signal which is applied to one input of a level comparator having the other input connected to receive the 19 kHz pilot signal extracted from the composite signal. The output of the comparator is sent to a level control circuit which controls the level of the signal supplied to the input of the inverting amplifier. Accordingly, the pilot signal is canceled in the signal sent to the switching circuit.

Abstract: A driver circuit that permits full duplex transmission of digital data on a single signal line includes means for enabling a receiver of a station having a transmitter and a receiver to ignore outgoing digital signals from the transmitter of the same station and receive incoming signals. The circuit includes means that combine the incoming and outgoing digital signals in the signal line to form a composite multi-level signal which shifts between predetermined amplitude levels and means that recover the incoming digital signals from the composite signal. An offset bias level is added within the receiver signal processing to the transmitter pulse level to reduce noise susceptibility. Using such a circuit a full duplex transmission system of a plurality of stations connected to a common single signal line is provided. Such a system can be operated in a broadcast mode wherein one station can transmit signals to the remainder of stations.