Abstract: A squelch circuit is provided with fast-acting means for unsequelching a receiver when a strong FM signal is received and for squelching a receiver when a strong FM signal is terminated. The squelch circuit is also provided with slow-acting means for unsquelching a receiver when a weak or slowly increasing FM signal is received and for squelching a receiver when a weak FM signal is terminated or when a strong or weak FM signal fades slowly.

Abstract: Compandor apparatus including a compressor comprised of an operational amplifier having a plurality of gain controlling feedback paths that are respectively responsive to different portions of the input frequency spectrum, and an expandor comprised of an operational amplifier having a plurality of gain controlling circuits that are respectively responsive to different portions of the input frequency spectrum.

Abstract: An automatic gain control amplifier having a controlled recovery of gain is disclosed and includes a peak detector for generating an output when the amplifier output exceeds a predetermined level, a memory setting circuit responsive to the peak detector output, a memory controlled by the memory setting circuit, and a memory adjust circuit responsive to information derived from the amplifier output. The output of the memory controls an attenuator of the automatic gain control amplifier. Amplifier output level change detection circuitry is also disclosed and accepts the output of the amplifier for producing an output indicating amplifier output level changes exceeding a predetermined magnitude. The level change detection output controls the memory adjust circuit.

Abstract: A field effect transistor that shunts a gain control resistor of an operational amplifier is slowly rendered conductive by charging a capacitor through a gate to source resistor and rapidly rendered non-conductive by a transistor connected in parallel with said capacitor so as to prevent undesired transients in the output of the amplifier when the gain is changed from one discrete level to another.

Abstract: A circuit for providing adaptive level control in a sound-recording device. A feed-back signal drives a variable attenuator which controls the input level to the audio amplifier stage. Means are provided for preventing voltage spikes at turn-on from adversely affecting the operation of the attenuator and which provide stable sensitivity control.

Abstract: A comparator is connected to the output of a variable gain amplifier and, when the output signal exceeds a predetermined threshold, pulses are applied to a plural stage shift register in series, with incremental voltages being generated in parallel at the outputs of the various stages. The incremental voltages are applied to the amplifier to vary the amplification thereof, and a threshold detector and timer also sense the output of the amplifier and reset the shift register when the output of the amplifier is below a predetermined value for at least preset period of time. One or more additional comparators may be included in the circuit to cause the shift register to activate one or more of the higher stages directly when the output of the amplifier exceeds a second predetermined amplitude. A step control circuit for shaping the response curve of the amplifier is also included.

Abstract: An electrical circuit for suppressing the effect of interfering alternating oltages of various frequencies superimposed upon a direct current signal in an electric measurand transmitter, such as in an electromechanical precision or fine balance, which comprises a signal line for carrying said direct current signal and interfering alternating voltages, means for low energy capacitively coupling-out of interfering alternating voltages of frequencies lower than a predetermined limit frequency from the signal line, means for energy amplifying and for inverting 180.degree. in phase said coupled-out voltages, and means for capacitively coupling-back into the signal line the amplified and inverted coupled-out voltages.

Abstract: An improved circuit for producing a signal indicative of an input signal floor level is disclosed for use in determining the noise level of an audio signal in a receiver voting system. An input audio signal which contains noise is amplified by variable gain amplifier circuitry consisting of a constant gain amplifier and a variable attenuator. Detector circuitry then develops a signal which is indicative of the noise level, this signal substantially corresponding to the minimum peak magnitude of the amplified input audio signal. During pauses between audio tones in the input audio signal, this minimum signal magnitude coincides the residual background noise level of the input audio signal. Control circuitry couples the noise level indicative signal to the variable attenuator and constitutes a negative feedback loop for inversely and nonlinearly varying the amplification of the input signal in response to the magnitude of the noise indicative signal.

Abstract: A fast-attack circuit is employed in an A.C. amplifier automatic gain control circuit to temporarily apply a D.C. gain control signal immediately to the amplifier circuit in response to a sudden signal increase in excess of a predetermined threshold level to avoid the problems of over-attack and pinch-down which might otherwise arise during the period required for the AGC loop to achieve stabilized control following the inception of the signal increase.

Abstract: A directional power detector mounted between the power amplifier and antenna which supplies audio frequency output signals indicative of forward and reflected power, circuitry for summing and converting the output signals from the power detector means to a DC potential proportional to the magnitude thereof and a transistor connected in shunt at the input of the power amplifier and controlled by the DC potential for controlling the peak envelope power at the antenna.

Abstract: In a signal compressor wherein an amplified and smoothed control signal is employed to control a variable gain or variable impedance device, a switch is provided to connect a positive feedback loop across the control signal amplifier, thereby to place the compressor in an oscillator mode for providing an alignment or calibration signal of stable amplitude.

Abstract: An automatic level controller comprising a switching transistor connected to the output stage of an audio amplifying circuit to be turned off when the output signal of the audio amplifying circuit attains a predetermined level, a control transistor connected to the input stage of the audio amplifying circuit for bypassing to the ground a portion of the audio signal applied to the audio amplifying circuit thereby controlling the audio level, a diode adapted to be turned on in response to the turn-off of the switching transistor for supplying current from a power source to the audio level control transistor as an audio level control signal, and a time constant circut for setting the attack period and release period of control by the audio level control signal.

Abstract: An audio compressor amplifier including an operational amplifier with compressor means connected from the output to the input for compressing signals at the output to a predetermined constant level in a predetermined attack time and including a plurality of diodes connected to reduce the series resistance in the compressor means for decreasing the attack time when the output signal exceeds the predetermined constant level by a predetermined amount, and a gain control feedback resistor connected from the output to the input of the operational amplifier and including a second resistor and a plurality of diodes connected in parallel therewith to reduce the gain of the operational amplifier and provide peak limiting action when a signal at the output exceeds a predetermined value in excess of the predetermined constant level.

Abstract: An rf level sensing circuit is described incorporating a pair of oppositely poled back diodes for receiving an rf signal. The diodes are connected to the two base inputs of a differential amplifier. A voltage divider comprising three series connected resistors is connected across a voltage supply. The junction of the first two resistors is connected to one of the bases and the junction of another two of the resistors is connected to one side of one of the back diodes. The collectors of the transistors are connected to the bases of a pair of complementary transistors which in turn drive the base of an output transistor. The collector of the output transistor is connected through a conventional diode to an output terminal; a parallel network comprising a capacitor and a resistor is connected between an output terminal side diode and ground.

Abstract: A noise reduction circuit for uncompressed and randomly compressed audio signals comprises a variable gain stage providing a gain which varies with the magnitude of a DC control signal fed to a control terminal thereby, an AC to DC converter for generating a DC signal proportional to the amplitude of the AC signal fed thereto and a filter for passing middle and upper frequencies and for eliminating or substantially reducing the low frequencies fed thereto and coupled between the audio signal input and the input to said AC to DC converter.

Abstract: A broadband automatic gain control amplifier is described incorporating a plurality of gain control loops, each responsive to signal levels at the output of the amplifier at different frequencies for developing a control signal to correct the output signal level simultaneously at that frequency and at other frequencies. Each of the gain control loops providing unique gain-frequency characteristic with respect to the other gain control loops.

Abstract: A dynamic expander which is particularly suitable for restoring the original dynamic range of prerecorded stereo sound program material is disclosed. In this embodiment, the expander comprises first and second variable gain amplifiers respectively coupled to a stereo input. The gain of the amplifiers is controlled by a common slow-attack, slow-decay time-constant circuit. An input of the time-constant circuit is coupled to the stereo input and the time-constant circuit responds thereto to provide a control signal which is indicative of the volume of the program material but which varies in accordance with the characteristics of a non-linear element in the time-constant circuit and with the slow-attack and slow-decay characteristics of the time-constant circuit. The control signal of the time-constant circuit drives a light-emitting-diode (LED) which, in turn, determines the resistance of a pair of matched, light-controlled-resistors (LCR's).

Abstract: A bistatic velocity detector system for underwater detection of objects of redetermined magnitude wherein the water may be capable of continual variations in velocity. The system includes a compensator that has an automatic gain controlled amplifier whose controlled output signal is applied first to an a.c./d.c. converter and then to an integrator circuit. A first voltage comparator receives the integrated signal to drive a relay for activating an alarm when a threshold is exceeded. A second voltage comparator having a lower reference voltage applied thereto drives an RC timer circuit whose output signal is applied to the gate of a field effect transistor of variable impedance for varying the gain of the operational amplifier. An alternative embodiment includes a dual gate transistor for use in the gain controlled amplification of the loop.