Abstract: The A.C. synthesizer is a unit developing several hundred watts at 60 Hz by ulse-width modulation techniques, with an 8 KHz sawtooth oscillator modulating a 60 Hz reference. Several failure modes common to electronic equipment caused the output stages designed for a pulse rate of 8 KHz to experience inputs from 60 Hz to as low as D.C., which inputs destroy expensive transistors. The addition of a retriggerable "one-shot" (monostable multivibrator) to inhibit the pulse width modulator output if not retriggered each 8 KHz cycle eliminates the catastrophic effect of most failure modes, allowing the output stage to reject low frequency pulses.

Abstract: An operational amplifier driver circuit for supplying an undistorted ac signal to a resistive load connected across a balanced pair of twisted transmission lines where the balanced lines have common mode noise signals thereon due to the presence of substantial noise of an external, uncontrolled nature. The driver circuit includes a pair of operational amplifiers interconnected to utilize the common mode noise signals in feedback paths thereof whereby the operational amplifiers are able to operate in their linear ranges even in the presence of high levels of common mode signals on the balanced lines, thereby compensating for the effects of the common mode noise signals on the balanced lines.

Abstract: A cable equalization resonant amplifier circuit for compensating for the signal-attenuation effects of a coaxial cable connected with the amplifier circuit and having a length of up to one-half mile. The gain of the amplifier circuit is matched with the attenuation characteristics of the coaxial cable over a wide range of frequencies by employing an LC resonant circuit with a Q of approximately 1 in the emitter circuit of an amplifying transistor. The gain for the amplifier circuit is established to match the attenuation characteristics of the coaxial cable at low frequencies by an RC circuit coupled with the amplifying transistor and the LC resonant circuit. The maximum or peak desired value of gain for the amplifier circuit at the resonant frequency of the LC resonant circuit is established by a resistor connected in series with the LC resonant circuit and a resistor in the collector circuit of the amplifying transistor.

Abstract: Apparatus for producing drive signals on any of several lines in response to input signals. Each of the lines has a drive circuit connected thereto. Resistances connected to the outputs of the drive circuits are connected together at a common juncture which acts as a summing point having a voltage proportional to the number of lines having drive signals thereon. First and second comparators are coupled to the common juncture and to threshold setting arrangements. The first comparator produces a signal if one or more of the lines has a drive signal and the second comparator produces a signal if two or more of the lines have signals. The outputs of the comparators are combined in alogic arrangement to produce an error signal if none of the lines has a signal or if two or more of the lines have signals. The threshold setting arrangements include a threshold setting drive circuit identical to the other drive circuits.

Abstract: Series voltage regulator including pass transistors connected between an input terminal and an output terminal. The voltage at the output terminal is stabilized by a feedback arrangement of a reference amplifier and coupling transistors connected between the output terminal and the bases of the pass transistors to control conduction through the pass transistors. A normally non-conducting protective transistor is connected between the bases of the pass transistors and ground. In the event the regulator is exposed to radiation, all the transistors become highly conductive. However, when the protective transistor becomes highly conductive, it biases the pass transistor to cutoff thus preventing the voltage at the output terminal from rising out of control.

Abstract: Communication switching system employing several stages of solid state crosspoint switching circuits. Biasing current is supplied to the SCR's of the switching circuits by biasing current control arrangements which provide a relatively heavy current to SCR's being turned on and a relatively low current sufficient to sustain conduction to operating SCR's subsequent to their being turned on.

Abstract: Apparatus is disclosed for sensing and determining whether or not exactly a predetermined proper number (N) of lines, part of a larger number of lines (M) are being driven, i.e., an "N of M Detector." It includes resistances connected to each of the lines, and connected together at a common summing point juncture, whose voltage is proportional to the number of lines being driven. The summing point is sensed by two comparators ("greater than" and "less than") followed by Exclusive Or logic which can deliver a "Not Exactly N" error signal. Also disclosed therewith is a transistor crosspoint switching array circuit.