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Signal transmission system and a transmitter and a receiver for use in the system

  • US 4,768,187 A
  • Filed: 06/30/1986
  • Issued: 08/30/1988
  • Est. Priority Date: 07/08/1985
  • Status: Expired due to Term
First Claim
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1. In a radio communication system comprising a plurality of transmitters transmitting signals to a plurality of receivers, the signals from respective transmitters being transmitted by modulating such signals on carrier waves having respective frequencies corresponding to respective message channels, each receiver receiving a signal in a message channel by direct conversion of the modulated signal in such channel to the frequency band of such signal, a method of operating of such system so as to separate the received signals from unwanted d.c. components produced by such direct conversion, such method comprising:

  • dividing the signal transmitted by each transmitter into complementary signals in respective frequency bands;

    dividing the message channel of each transmitter into a pair of sub-channels in separate frequency bands symmetrically located above and below a carrier frequency assigned to such message channel, and modulating the respective complementary signals to translate them into the respective sub-channels;

    assigning carrier frequencies to the respective transmitters in said system such that the sub-channels of any transmitter message channel are interleaved with a sub-channel of a message channel of least one of the other transmitter in said system;

    tuning each receiver to the carrier frequency of a message channel to be received by such receiver;

    each receiver directly recovering the complementary signals in the sub-channels of a received channel by converting the modulated signals in such sub-channels to the frequency bands of such complementary signals, and combining the frequency bands of the recovered complementary signals to derive a combined signal, the frequency band of such combined signal being separated from d.c.; and

    band-pass filtering said combined signal to separate it from other signals in the received message channel, such filtering also blocking any d.c. component of said combined signal.

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