Showing papers on "Continuous phase modulation published in 1975"

Optimizing the PWM Waveform of a Thyristor Inverter

Abstract: An optimization method, which will be of use in selecting the modulation technique and Carrier frequency for a PWM inverter system, is presented. The difficult decision, concerning the tradeoff between efficiency and unfiltered harmonic content, can be made with the help of this method. A relation between second-order filter rating and unfiltered harmonic attentuation, for optimum component values, is also obtained. The optimization method is used for illustration to select the optimum modulation technique and its carrier frequency for the modified McMurray inverter [1] to be used in a rapid transit auxiliary power converter. The design aim is to obtain a constant sine wave output with a specific input supply voltage variation. The inverter efficiency is predicted for various carrier frequencies using two modulation schemes. The Schonung and Stemmler [2] modulation approach, with a carrier frequency of 900 Hz, is found to be optimum as it results in low filter rating and an efficient inverter.

Double sideband transmission system

Abstract: An improved system and method for processing and amplifying double-sideband suppressed or reduced carrier waves using high efficiency amplifiers and not requiring frequency dividers. Typical practice of the invention involves generating a double-sideband suppressed carrier wave in a balanced modulator; for example, at a sub-harmonic carrier frequency and multiplying the frequency of the output of the balanced modulator by an odd multiplication factor greater than one in the modulated amplifier. The required envelope modulation (amplitude modulation) component is derived from the original balanced modulator output by use of an envelope demodulator and the component is used to modulate the modulated stage so as to reproduce the double-sideband suppressed carrier wave at a high power level. This invention may also be used in reduced carrier double-sideband transmitters; i.e., where the carrier is not fully suppressed but where the carrier is smaller in amplitude than the peak amplitude of the combined upper and lower sideband waves.

Methods and apparatus for speed-control of induction motors

Abstract: A method of energizing a single-, three-, or poly-phase A.C. motor for continuously-variable speed control from a fixed-frequency supply of corresponding phase. Each phase is modulated by a continuously-variable modulation wave of sub-supply frequency to provide two continuously-variable sideband frequencies, either of which can be used to supply the motor. The modulation wave is sampled in each cycle of the A.C. supply and a full-wave rectified resultant modulation wave compared with a cosine wave of supply frequency. Each phase is gated by solid-state switch means for current flow from amplitude equality to next-following cosine zero. Optionally, secondary modulation, by a square wave of supply frequency, is used.

Narrowband phase modulation communication system which eliminates thresholding

Abstract: A narrowband phase modulation communication system is disclosed which eliminates thresholding At the transmitter, quadrature modulation which produces very large maximum phase deviation is employed in conjunction with a constant amplitude limiter The constant amplitude resultant contains the carrier and voice signal components in quadrature and is transmitted, at a suitable frequency, in this form At the receiver, a narrowband phase locked loop is employed for demodulation This demodulating loop coherently tracks the carrier component and eliminates the thresholding problem normally encountered In a modification, the carrier component is used to transmit data either alone or in combination with the voice signal

Coherent phase demodulator for phase shift keyed suppressed carrier signals

Abstract: Digital data, differentially phase shift keyed on a suppressed carrier, double side band transmission, is recovered by multiplying the input signal by a signal derived from regenerative feedback and consisting of the sum of a phase-coherent carrier and the recovered data signal. The phase-coherent carrier is derived by alternate phase reversals of the incoming carrier, produced by the polarity changes in the data. The phase-coherent carrier and the recovered data signal are components of the multiplier output and are separated by bandpass and low pass filters respectively, the output terminal of the low pass filter also being the data output terminal. When a carrier has been phase modulated with two distinct signals in quadrature, the received carrier is phase shifted to produce two signals in quadrature, then each of the resultant modulated carriers is demodulated as with the single signal carrier, using one common bandpass filter.

Color television recording system employing frequency modulation and pulse width modulation

Abstract: A color television system for transmitting a color television signal, specifically for recording on and subsequently reproducing from a record carrier. The color television signal to be transmitted contains a first carrier which is frequency-modulated with the luminance information and a second carrier which is modulated with the chrominance information, whose frequency lies between zero and the first-order lower side band of the modulated first carrier which corresponds to the highest modulation frequency. Said second carrier does not have a fixed frequency, but is locked to the instantaneous frequency of the modulated first carrier by a constant integral ratio. Depending on the characteristics of the transmission medium and the signal processing equipment said ratio is preferably two or three.

Modulator for tone and binary signals

Abstract: Tones and binary information are transmitted as phase variations on a carrier wave of constant amplitude and frequency The carrier and tones are applied to a balanced modulator for deriving an output signal including a pair of sidebands relative to the carrier The carrier is phase modulated by a digital signal so that it is + or - 90 deg out of phase with the predetermined phase of the carrier The carrier is combined in an algebraic summing device with the phase modulated signal and the balanced modulator output signal The output of the algebraic summing device is hard limited to derive a constant amplitude and frequency signal having very narrow bandwidth requirements At a receiver, the tones and binary data are detected with a phase locked loop having a voltage controlled oscillator driving a pair of orthogonal detection channels

Microwave QPSK Demodulation Techniques at the Receiver Front End

Abstract: Quadriphase modulation of microwave or mm-wave carriers involves the rapid shifting of the phase of the carrier between one of four orthogonal positions by binary data included on two parallel data streams. The received quadriphase (QPSK) carrier can be demodulated by mixing this carrier with an appropriately phased local oscillator signal in a doubly-balanced mixer. One of the problems in demodulation of quadriphase carriers is the generation of the local oscillator having carrier frequency and phase information. This can be accomplished either at RF from the incoming QPSK carrier or at baseband by comparing the crosstalk associated with the two demodulated data streams, This paper will describe the applicable microwave technologies utilizing special quadruple frequency multipliers which provide microwave carrier reconstruction which facilitates the demodulation of data information from the carrier.

A comparison of two digital modulation schemes

Abstract: The 4-phase PSK and the Fast FSK are two different digital modulation systems; both perform well when it is required to conserve power as well as bandwidth. This report discusses some of the subtle differences between their signal structures, their spectral occupancy, and between the circuitry which "self synchronizes", i.e. regenerates carrier phase and clock references at their receivers.

Spectra and performance of biternary phase modulation

Abstract: The spectra and performance of a biternary phase-shift-keyed system are presented, and comparisons with the binary phase-shift-keyed system of the same data rate and system bandwidth are made.