Narrowband phase modulation communication system which eliminates thresholding
AssigneeTextron Inc.
InventorTheodore Lerner
Life of this patent
Estimating the term…
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.
Claims5
A narrowband phase modulation voice communication system characterized by the absence of thresholding effects at useful signal-to-noise ratios, comprising in combination:
- transmitter means for transmitting a signal having a voice signal component and receiver means for receiving the transmitted signal;
- said transmitter means including carrier signal generator means for generating a carrier signal of fixed amplitude, voice signal input means for generating a voice signal, and phase modulator means connected to said carrier signal and to said voice signal for producing a resultant signal in the form of a variable amplitude resultant signal having a voice signal component and a fixed amplitude carrier signal component in phase quadrature, said voice signal component having a maximum amplitude whereby said resultant signal has a maximum phase deviation .phi. which is large with respect to but less than 90.degree. such that sin .phi..noteq..phi., and limiter means connected to said phase modulator means for limiting said resultant signal to a constant amplitude signal whereby said carrier signal component is of variable amplitude and said voice signal component is attenuated;
- and
- said receiver means including phase locked loop demodulator means for coherently tracking said variable amplitude carrier component to recover said attenuated voice signal component.
The method of voice communicating by means of radiant energy transmission and reception, which comprises the steps of:
- a. phase modulating a sinusoidal carrier signal with a voice signal to produce a resultant signal which consists of said carrier signal and said voice signal as quadrature components, the maximum amplitude of said voice signal component being sufficiently large with respect to said carrier signal component that the maximum phase deviation .phi. of said resultant signal with respect to the carrier signal component is less than but large with respect to 90.degree. so that sin .phi..noteq..phi.;
- b. hard limiting said resultant signal to provide a constant amplitude resultant signal;
- c. transmitting said constant amplitude resultant signal at a selected frequency;
- d. receiving the transmitted signal;
- and
- e. demodulating the received signal by coherently tracking its carrier component while recovering its voice signal component whereby the demodulation process is unaffected by thresholding.
Dependencies are inferred from the claim text.