Gte Lenkurt Electric (canada) Ltd.

Gte Automatic Electric Laboratories Incorporated

Ael Microtel, Ltd.

Gte Lenkurt (canada) Ltd.

Christopher R Huntley

To minimize carrier leak in the modulation of voice frequencies to the desired line frequency for a carrier system, a first balanced modulator is operated at a low frequency where low carrier-leak modulators may be constructed and a second balanced modulator, directly coupled to the first, is employed. The modulation frequency of said second modulator is very high compared to that of said low-frequency modulator. The sideband obtained from the second modulation stage is remote from said high-frequency carrier and a band-pass filter selects the desired sideband and substantially eliminates the high-frequency carrier and the other sideband. Thus, only a low amplitude of carrier leak is present which may cause interference with other channels.

Modulator utilizing high and low frequency carriers

First and second NPN transistors are direct connected in an astable multivibrator configuration. Each collector is connected to the positive terminal of a DC power source through series connected diodes. A resistor, which is selected to control the amplitude of oscillation, is connected between the collectors. The frequency of oscillation is controlled by a frequency determining component which is connected between the emitters of said transistors. The emitters are connected to current sources.

Monolithic astable multivibrator circuit

A network simulating an ungrounded inductor includes an active gyrator circuit which employs an operational amplifier, said gyrator being a two port device having an ungrounded port, and a grounded port. The ungrounded port is terminated in a capacitor C so as to provide an input impedance, Zin, looking into the grounded port, which simulates an inductor: Zin=e1/i1=j.omega.R.sup.2 C, where .omega.=2.pi.f, e1 the voltage across the port and i1 is the current into the port. A current i2 is developed in the gyrator circuit, from the operational amplifier output, and appears as an extraneous current at the grounded terminal of the grounded port. An active network including a second operational amplifier is connected to the active gyrator circuit and is arranged to provide a current i3 which is equal in value to but opposite in sign from said i2 current. The current i3 is combined with the i1 and i2 currents at the grounded terminal. Because of its amplitude and sign the current i3 effectively cancels the i2 current. Thus, only the current i1 appears to pass into and out from the terminals of the grounded port and a simulated ungrounded inductor is obtained.

Floating gyrator having a current cancellation circuit

A double sideband suppressed carrier (DSBSC) modulator for operation from unbalanced carrier frequency and modulation frequency sources has the input terminals of first and second constant current amplifiers connected to receive the modulation frequency output signal from the unbalanced source. The first and second constant current amplifiers provide in-phase and out-of-phase modulation frequency signals at respective high impedance output terminals for connection to a modulator. The modulator comprises a quad, i.e., four transistors connected to provide a pair of differential amplifiers. Transistors 1 and 2 comprising the first of the pair and transistors 3 and 4 comprising the second of the differential pair. The emitters of each differential amplifier are tied together. The emitter junction of the first differential amplifier is connected to the high impedance output of the first constant current amplifier, and the emitter junction of the second differential amplifier is connected to the high impedance output of the second constant current amplifier. The base of transistors 2 and 3 are connected together and then connected to one terminal of the carrier frequency source. The bases of transistors 1 and 4 are connected together and then connected to the other terminal of the carrier frequency source. The collectors of transistors 1 and 3 are tied together and the collectors of transistors 2 and 4 are tied together to provide the modulated signal output paths.

Low-distortion double sideband suppressed carrier monolithic modulator

The disclosed voltage regulator circuit provides a regulated direct output voltage, across first and second output terminals, when an unregulated direct input voltage is applied across first and second input terminals. The second terminals are common to both input and output connections. A voltage reference device, having first and second electrodes, is connected so that the second electrode is connected to the second terminals. A first DC amplifier has an input circuit connected between the first input terminals and the first electrode, and an output circuit connected between the first output terminals and the first electrode. A second DC amplifier has an input circuit connected to the input circuit of the first DC amplifier and an output circuit connected to the output circuit of the first DC amplifier. The second DC amplifier, besides sharing the current load requirements with the first DC amplifier, also controls a bias current through the voltage reference device. The voltage reference device provides both amplifiers with a constant reference voltage enabling the amplifiers to maintain a constant output voltage despite changes in input line voltage.

Low dissipation voltage regulator

The square-wave output of a comparator is coupled back to the input of an RC controlled integrator including an operational amplifier and an inverter circuit with an output signal maintained at a predetermined level. The RC network sets the pulse repetition rate of the square wave. The inverter and integrator outputs are connected to separate inputs of the comparator. A gating circuit couples a data source to the operational amplifier. In particular, the gating circuit couples an additional square-wave current to the integrator via a resistor. The square-wave current may be in phase and raise the pulse repetition rate of the resulting square wave or out of phase and lower the pulse repetition rate.

Digital frequency shift-keyed transmitter

A receiver is provided for utilization in a protective relaying modem to effectively distinguish between two mutually exclusive signal frequencies in a given frequency channel and which are respectively indicative of a 'fault' or 'no-fault' condition in a remote power transmission line. The received signals are coupled to a channel detector which utilizes a local oscillator and mixers to translate the received signal down in frequency so that simple low pass filters can isolate the desired frequency channel. The outputs of the low pass filters are operated on by a combination of multipliers and differentiators to generate an AM related output and a FM related output. The FM signal output of the channel detector is DC in nature and has an amplitude proportional to the deviation of the received signal frequency from the center frequency of the channel. This signal is used by separation circuitry to ascertain a fault or no-fault condition. The AM output is a DC signal that is proportional to the strength of the received signal and is analyzed to determine if the originally received signal was generated or unacceptably affected by electronic noise. If the noise content does not fall within the predeterminably set limits, any 'fault' condition signal is automatically inhibited until the validity of such signal can be ascertained. The detection time for ascertaining whether a valid fault signal has been received can be adjusted to achieve a minimum yet effective detection time. The output of the receiver indicating a fault condition can be utilized to control various circuit breakers in the power transmission system.

Growing community of inventors

Burnaby, Canada

Christopher R Huntley