NDLI: Selective Demodulation

Content Provider	IEEE Xplore Digital Library
Author	Harris, D.B.
Copyright Year	1931
Abstract	A method of demodulation is proposed in which the output current of the demodulator is a linear function of the input voltage, while at the same time provision is made for producing the necessary product terms which will result in demodulation. Demodulation is brought about by integrating the product of the instantaneous value of the modulated wave by the instantaneous value of a wave having the same frequency and phase as the carrier. Where this method of demodulation is used it is proposed that two carriers in quadrature on the same frequency may be employed, reducing the bandwidth to that required for single-sideband transmission. It is suggested that the required linear demodulation characteristics may be obtained through the use of "electron-coupled" demodulators. Theoretical considerations indicate that, when demodulation of this type is employed, selectivity ahead of the demodulator may be dispensed with, the signal-to-noise ratio is improved, greater economy of spectrum space is obtained, the number of tubes required is materially reduced through the use of a common intermediatefrequency amplifier for a number of channels, and any impairment due to the instability of the carrier or oscillator frequency is reduced. As an example of the possible application of the principles outlined, a hypothetical eight-channel transmission system is described.
Starting Page	565
Ending Page	572
Page Count	8
File Size	1880809
File Format	PDF
ISSN	00968390
Volume Number	35
Issue Number	6
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	1947-06-01
Access Restriction	Subscribed
Rights Holder	The Institute of Radio Engineers, Inc. (IRE)
Subject Keyword	Demodulation Frequency Phase modulation Voltage Oscillators Senior members Bandwidth Signal to noise ratio Telephony Equations
Content Type	Text
Resource Type	Article
Subject	Electrical and Electronic Engineering

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