Modified vestigial side band transmission system
First Claim
1. A telephone transmission system providing multiple modulated carrier communication channels between a single central station and plural remote stations on a single transmission medium which exhibits phase nonlinearities at certain frequencies, comprising:
- plural transmitters at said central and remote stations, each generating on said transmission medium double side band AM modulated communication signals at different carrier frequencies; and
plural receivers at said central and remote stations, each tuned to one of said different carrier frequencies on said transmission medium, at least one of said plural receivers, which receiver is tuned to receive the double side band AM modulated communication signal from one of said plural transmitters, and which receiver is tuned to one of said certain frequencies which exhibit phase nonlinearities, attenuating at least a portion of one of said double side bands more than the corresponding portion of the other of said side bands to eliminate side band phase cancellation.
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0 Petitions
Accused Products
Abstract
A communication transmission system includes one or more modulated carrier communication channels in which a receiver has a modified vestigial side band filter for eliminating phase cancellation. Accurate design of the modified vestigial side band filters at the receivers, further reduces susceptibility to frequency drift caused by component aging and component response to environmental changes. The system has particular utility in multiple channel carrier telephone communication systems which utilize limited available band width for providing a maximum number of communication channels over an extended length communication line.
30 Citations
42 Claims
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1. A telephone transmission system providing multiple modulated carrier communication channels between a single central station and plural remote stations on a single transmission medium which exhibits phase nonlinearities at certain frequencies, comprising:
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plural transmitters at said central and remote stations, each generating on said transmission medium double side band AM modulated communication signals at different carrier frequencies; and plural receivers at said central and remote stations, each tuned to one of said different carrier frequencies on said transmission medium, at least one of said plural receivers, which receiver is tuned to receive the double side band AM modulated communication signal from one of said plural transmitters, and which receiver is tuned to one of said certain frequencies which exhibit phase nonlinearities, attenuating at least a portion of one of said double side bands more than the corresponding portion of the other of said side bands to eliminate side band phase cancellation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of carrier multiplexing multiple telephone communication channels between a single central station and plural remote stations on a single communication medium exhibiting phase nonlinearities at a certain frequency, comprising:
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transmitting said multiple channels from said central and remote stations on said communication medium as double side band AM modulated carrier signals having carriers at different frequencies; and avoiding communication medium induced distortion at said certain frequency by receiving at least some modulation frequencies on said communication medium of at least one of said multiple double side band AM modulated channels at one of said central or remote stations as a single side band AM modulation signal. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A receiver filtering method used with a carrier multiplexed, double side band transmission, comprising:
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receiving a modulated carrier of said carrier multiplexed, double side band transmission from a transmission medium at a carrier frequency at which said medium exhibits phase nonlinearities; attenuating a first side band of said carrier to a greater extent than a second side band of said carrier at frequencies displaced from said carrier by less than a first amount; essentially eliminating said first side band of said carrier, in comparison with said second side band of said carrier, at frequencies displaced from said carrier by more than a second amount; and using a filter having an attenuation versus frequency slope at said carrier low enough to be effective in avoiding frequency drift induced distortion. - View Dependent Claims (16, 17, 18, 19)
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20. A method of designing a carrier multiplexed, multiple channel transmission system, for use with a transmission medium having nonlinear phase characteristics at certain frequencies comprising:
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selecting carrier frequencies for double side band AM transmission of each of said multiple channels; determining the frequencies at which said transmission medium exhibits acute nonlinear phase characteristics; designing first double side band AM receivers for frequencies at which said transmission medium does not exhibit acute nonlinear phease characteristics; and designing second receivers which attenuate at least a portion of one side band more than the corresponding portion of the other side band for said frequencies at which said transmission medium exhibits acute nonlinear phase characteristics. - View Dependent Claims (21, 22, 23, 24)
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25. A receiver filter used with a double side band, AM modulated carrier signal in a carrier multiplexed telephone transmission system used for communicating telephone signals between a single central office terminal and plural remote subscriber terminals on a single communication medium, said filter tuned to a communication frequency at which said medium exhibits phase nonlinearities, comprising:
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means for providing a pass band frequency displaced on both sides of said carrier signal; and means for attenuating said double side band, AM modulated carrier to a greater extent at frequencies within said pass band displaced in one direction from said carrier signal than at frequencies within said pass band displaced by an equal amount in the other direction from said carrier signal. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 33)
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34. A carrier multiplexed telephone transmission system, comprising:
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a pair of transmission lines; plural central office channels, each comprising; a transmitter for generating on said pair of transmission lines a double side band AM modulated carrier output signal carrying voice information; and a receiver for receiving AM modulated carrier signals from said pair of transmission lines to demodulate voice information;
plural subscriber channels, each comprising;a transmitter for generating through said pair of transmission lines a double side band AM modulated carrier output signal carrying voice information; and a receiver for receiving AM modulated carrier signals from said pair of transmission lines to demodulate voice information;
at least one of said central office andsubscriber channel receivers demodulating both the upper and lower side bands of said AM modulated carrier; and - View Dependent Claims (36, 37, 38, 39, 40, 41)
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35. at least one other of said central office and subscriber channel receivers, which is tuned to a frequency at which said transmission lines exhibit phase nonlinearities, demodulating one side band to the substantial exclusion of the other side band of said AM modulated carrier at selected modulation frequencies.
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42. A telephone transmission system providing multiple modulated carrier communication channels between a single central station and plural remote stations on a single transmission medium, comprising:
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a transmitter for modulating a carrier signal to provide one of said communication channels; a receiver for demodulating said one of said communication channels; a filter in said communication channel providing a pass band which; (a) provides substantially double side band communication on said channel at modulation frequencies below a first predetermined frequency; (b) provides substantially single side band communication on said channel at modulation frequencies above a second predetermined frequency; (c) provides approximately 3.5 db attenuation of said carrier signal with respect to the least attenuated modulation frequencies.
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Specification