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Showing papers on "Quadrature amplitude modulation published in 1968"


Journal ArticleDOI
TL;DR: In this paper, the quadrature components of the signal are represented explicitly by lowpass interpolation formulas that greatly facilitate digital processing of signal when compared to commonly used sampling formulas.
Abstract: The quadrature sampling technique, which obtains samples of the quadrature components of a high‐frequency band‐limited waveform by direct sampling of the waveform, is shown to lead to an exact interpolation formula. In this formula, the quadrature components of the signal are represented explicitly by low‐pass interpolation formulas that greatly facilitate digital processing of the signal when compared to commonly used sampling formulas. For example, the amplitude modulation (envelope) and phase modulation of a signal can be computed directly from these quadrature components.

55 citations


Patent
18 Nov 1968
TL;DR: In this paper, the authors present a scenario in which a parallel legged-connected resistant resistant robot is connected with a human-controlled OSCILLATOR TANK CIRCUIT to prevent the current flow through the robot without physically disconnecting it from the tank.
Abstract: IN FREQUENCY-SHIFT KEYING A SIGNAL WITH A TRANSISTOR KEYING DEVICE, PHASE SHIFT AT THE INSTANT OF KEYING IS AVOIDED BY CONNECTING, IN PARALLEL WITH THE OSCILLATOR TANK CIRCUIT, A REACTANCE IN SERIES WITH A PARALLEL-CONNECTED RESISTORAND-UNITY-GAIN-AMPLIFIER COMBINATION SO THAT ENERGIZATION OF THE UNITY GAIN AMPLIFIER PREVENTS CURRENT FLOW THROUGH THE RESISTOR WITHOUT PHYSICALLY DISCONNECTING IT FROM THE CIRCUIT.

3 citations


Patent
26 Aug 1968

3 citations


Journal ArticleDOI
TL;DR: It is concluded that a Q-PSK system can be used effectively only in a decision-directed mode and is limited by self-noise unless certain message sequences can be avoided.
Abstract: In this paper we exhibit the effect of the data sequence on the reconstruction of the reference (pilot) tone for a quadrature phase-shift keying (Q-PSK) system. This is a binary digital transmission system in which the phase of one quadrature component of the carrier tone is keyed, while the phase of the other component is unkeyed. The integration of several previous keying intervals provides a reference phase. A scheme of this type, called Kathryn, has been built by General Atronics Corporation. We find that the performance of a Q-PSK system is limited by self-noise unless certain message sequences can be avoided. It is concluded that a Q-PSK system can be used effectively only in a decision-directed mode which is also analyzed.

2 citations


Journal ArticleDOI
TL;DR: A digital computer simulation of a noise-free frequency-shift keying (FSK) data system that consists of a frequency modulator, a send and receive bandpass filter, a limiter, and a frequency demodulator is described.
Abstract: A digital computer simulation of a noise-free frequency-shift keying (FSK) data system is described. This system consists of a frequency modulator, a send and receive bandpass filter, a limiter, and a frequency demodulator. The simulation is used to study the performance of the system in terms of telegraph distortion for various filters and demodulators. The accumulated spectral density of the modulated Q 9S test signal is examined. The modeling of the system and the processing of the test signal are discussed.

1 citations


Proceedings ArticleDOI
20 May 1968
TL;DR: In this paper, a simple circuit for a reflection type modulator is obtained when the diode terminates a transmission line, then the phase of the reflected wave can be shifted by a change of the bias voltage.
Abstract: For communication by radio links, satellites, waveguides etc. a pulse code modulation that is realized by phase reversal (phase shift keyed) has advantages as compared to a pulse amplitude modulation because the signal-to-noise ratio can be 6 db less for the same error probability. The phase shift keying of the microwaves should be rapid (< 1ns) and the modulation losses should be small. A suitable semiconductor element for such a phase modulator is a voltage dependent capacitance diode. A simple circuit for a reflection type modulator is obtained when the diode terminates a transmission line. Then the phase of the reflected wave can be shifted by a change of the bias voltage. The lossless tuner in figure 1a is adjusted so that any residual amplitude modulation is minimized.

1 citations