Frequency-division multiplex communications system having grouped transmitters and receivers

Claim 1

A communications system comprising a multiplicity of communications terminals, said terminals including receive-only terminals having receivers, send-only terminals having transmitters, and transceivers having both a transmitter and a receiver; and a bus to which said terminals are coupled for purposes of intercommunication; wherein said multiplicity of terminals are partitioned into a plurality of groups, each of said groups comprising: a plurality of fixed frequency receivers each tuned to receive signals modulating a single, different carrier frequency, wherein all of the carrier frequencies to which said plurality of receivers are tuned are closely spaced within a narrow frequency band, said narrow frequency band being exclusive among all of said groups; a plurality of transmitters for transmitting signals on a carrier frequency, each of said plurality of transmitters adapted to transmit on all of the carrier frequencies within all of said narrow frequency bands of said system; first combining means for combining the output signals of said plurality of transmitters; a first filter coupled to said first combining means for passing only those signals having a carrier frequency not substantially higher than the highest carrier frequency transmitted by said transmitters; means for coupling the signals passed by said first filter to said bus and for receiving signals transmitted along said bus; a second filter coupled to said coupling means for passing only those signals received from said bus having carrier frequencies not substantially outside said narrow frequency band; and means for coupling the signals passed by said second filter to each of said plurality of receivers.