Frequency multiplexed telephone system

Claim 2

A frequency division multiplexed telephone system for connection to a subscriber telephone line, said system comprising: a common conductor cable; a line adapter unit for coupling said common conductor cable to said subscriber telephone line, and having a pilot tone generator for producing a pilot tone signal on said common conductor cable; and a plurality of telephone sets coupled to said cable for producing frequency division multiplexed signals on said cable, each of said telephone sets including: a clock for producing a clock signal having a clock frequency; a frequency divider coupled to said clock for dividing said clock signal to produce a digital carrier signal having a frequency that is a sub-multiple of said clock frequency; a phase detector coupled to said cable for detecting the phase of said pilot tone signal; a controller connecting said frequency divider to said phase detector for causing said frequency divider to generate said carrier signal in phase with said pilot tone signal; and a modulator coupled to said common conductor cable and to said frequency divider for modulating a voice signal onto said carrier signal.

Claim 3

The frequency division multiplexed telephone system of claim 1, wherein each of said telephone sets additionally includes a demodulator coupled to said common conductor cable and to the output of said frequency divider for demodulating signals received from said cable.

Claim 4

The frequency division multiplexed telephone system of claim 2, wherein each of said telephone sets additionally includes a phase delay coupled between the output of said frequency divider and said demodulator for phase-delaying said digital carrier signal amount corresponding to the phase delay experienced by a signal propagating along said common conductor cable.

Claim 5

The frequency division multiplexed telephone system of claim 1, wherein each of said telephone sets additionally includes a mode selector coupled to said frequency divider for setting the frequency of said digital carrier signal.

Claim 6

A frequency division multiplexed telephone system for connection to a subscriber telephone line, the system comprising: a common conductor cable; a line adapter unit for coupling said common conductor cable to said subscriber telephone line, and having a pilot tone signal generator for producing a pilot tone on said common conductor cable; and a plurality of telephone sets coupled to said cable for producing frequency division multiplexed signals on said cable, each of said telephone sets including: a phase detector coupled to said cable for detecting the phase of said pilot tone signal; a clock for producing a clock signal having a clock frequency; a carrier generator connected to said clock for dividing said clock signal to produce a carrier signal having a frequency that is a sub-multiple of said clock frequency; a voltage-controlled oscillator connecting said carrier generator to said phase detector so that the carrier signal developed by said carrier signal generator is in phase synchronism with said pilot tone signal; a modulator coupled to said carrier generator for modulating a voice signal onto said carrier signal; a phase delay coupled to said carrier generator for phase-delaying said carrier signal an amount corresponding to the phase delay experienced by a signal propagating along said common conductor cable; and a demodulator coupled to said common conductor cable and to the output of said phase delay for demodulating signals received from said cable.

Claim 7

A frequency division multiplexed telephone system for connection to a subscriber telephone line, the system comprising: a common conductor cable; a line adapter unit for coupling said common conductor cable to said subscriber telephone line, and having a pilot tone signal generator for producing a pilot tone on said common conductor cable; and a plurality of telephone sets coupled to said cable for producing frequency division multiplexed signals on said cable, each of said telephone sets including: a phase detector coupled to said cable for detecting the phase of said pilot tone signal; a clock for producing a clock signal having a clock frequency; a carrier generator connected to said clock for dividing said clock signal to produce a carrier signal having a frequency that is a sub-multiple of said clock frequency; a voltage-controlled oscillator connecting said carrier generator to said phase detector so that the carrier signal developed by said carrier signal generator is in phase synchronism with said pilot tone signal; a modulator coupled to said carrier generator for modulating a voice signal onto said carrier signal; a phase delay coupled to said carrier generator for phase-delaying said carrier signal an amount corresponding to the phase delay experienced by a signal propagating along said common conductor cable; and a demodulator coupled to said common conductor cable and to the output of said phase delay for demodulating signals received from said cable.

Claim 8

A frequency division multiplexed telephone system for connection to a subscriber telephone line, said system comprising: a common conductor cable; a line adapter unit for coupling said common conductor cable to said subscriber telephone line, and having a pilot tone generator for producing a pilot tone signal on said common conductor cable; and a plurality of telephone sets coupled to said cable for producing frequency division multiplexed signals on said cable, each of said telephone sets including: a pilot tone receiver for detecting said pilot tone on said common conductor cable and for supplying a local reference signal in accordance therewith; a carrier signal generator responsive to a clock signal for generating a carrier signal having a frequency that is a sub-multiple of the frequency of said clock signal, and responsive to said local reference signal so that said carrier signal is in phase synchronism with said pilot tone signal; a handset; a modulator connected to said carrier signal generator, to said common conductor cable, and to said handset for modulating voice signals from said handset onto said carrier signal and transmitting the modulated signal to said cable; and a demodulator connected to said handset, to said common conductor cable, and to said carrier signal generator for demodulating signals received from said common conductor cable into voice signals and transmitting said voice signals to said handset.

Claim 9

A frequency division multiplexed telephone system for connection to a subscriber telephone line, said system comprising: a common conductor cable; a line adapter unit for coupling said common conductor cable to said subscriber telephone line, and having a pilot tone generator for producing a pilot tone signal on said common conductor cable; and a plurality of telephone sets coupled to said cable for producing frequency division multiplexed signals on said cable, each of said telephone sets including: a pilot tone receiver for detecting said pilot tone on said common conductor cable and for supplying a local reference signal in accordance therewith; a carrier signal generator responsive to a clock signal for generating a carrier signal having a frequency that is a sub-multiple of the frequency of said clock signal, and responsive to said local reference signal so that said carrier signal is in phase synchronism with said pilot tone signal; a handset; a modulator connected to said carrier signal generator, to said common conductor cable, and to said handset for modulating voice signals from said handset onto said carrier signal and transmitting the modulated signal to said cable; and a demodulator connected to said handset, to said common conductor cable, and to said carrier signal generator for demodulating signals received from said common conductor cable into voice signals and transmitting said voice signals to said handset.

Claim 10

The frequency division multiplexed telephone system of claim 6, wherein each of said telephone sets additionally comprises a voice frequency low-pass filter connected to the input of said modulator for bandlimiting voice signals input to said modulator.

Claim 11

A frequency division multiplexed telephone system for connection to a subscriber telephone line, said system comprising: a common conductor cable; a line adapter unit for coupling said common conductor cable to said subscriber telephone line, and having a pilot tone generator for producing a pilot tone signal on said common conductor cable; and a plurality of telephone sets coupled to said cable for producing frequency division multiplexed signals on said cable, each of said telephone sets including: a clock for producing a clock signal having a clock frequency; a pilot signal bandpass filter coupled to said common conductor cable for passing said pilot tone signal; a phase detector coupled to the output of said pilot signal bandpass filter for detecting the phase of said pilot tone signal; a carrier generator connected to said clock for dividing said clock signal to produce a digital carrier signal having a frequency that is a sub-multiple of said clock frequency; a modulator coupled to the output of said carrier generator for modulating a voice signal onto said carrier signal; a voltage-controlled oscillator connecting said phase detector to said carrier generator so that said carrier generator generates said carrier signal in phase synchronism with said pilot tone signal; carrier frequency select means connected to said carrier generator for setting the frequency of said carrier signal generated by said carrier generator; a phase delay coupled to the output of said carrier generator for phase-delaying said carrier signal an amount corresponding to the phase delay experienced by a signal propagating along said common conductor cable; a demodulator coupled to said common conductor cable and to the output of said phase delay for demodulating signals received from said cable; a handset; a first voice frequency low-pass filter connected between said handset and said modulator for bandlimiting voice signals received from said handset; and a second voice frequency low-pass filter connected between the output of said demodulator and said handset for filtering voice signals transmitted from said demodulator to said handset.

Claim 12

A frequency division multiplexed telephone system for connection to a subscriber telephone line, said system comprising: a common conductor cable; a line adapter unit for coupling said common conductor cable to said subscriber telephone line, and having a pilot tone generator for producing a pilot tone signal on said common conductor cable; and a plurality of telephone sets coupled to said cable for producing frequency division multiplexed signals on said cable, each of said telephone sets including: a clock for producing a clock signal having a clock frequency; a pilot signal bandpass filter coupled to said common conductor cable for passing said pilot tone signal; a phase detector coupled to the output of said pilot signal bandpass filter for detecting the phase of said pilot tone signal; a carrier generator connected to said clock for dividing said clock signal to produce a digital carrier signal having a frequency that is a sub-multiple of said clock frequency; a modulator coupled to the output of said carrier generator for modulating a voice signal onto said carrier signal; a voltage-controlled oscillator connecting said phase detector to said carrier generator so that said carrier generator generates said carrier signal in phase synchronism with said pilot tone signal; carrier frequency select means connected to said carrier generator for setting the frequency of said carrier signal generated by said carrier generator; a phase delay coupled to the output of said carrier generator for phase-delaying said carrier signal an amount corresponding to the phase delay experienced by a signal propagating along said common conductor cable; a demodulator coupled to said common conductor cable and to the output of said phase delay for demodulating signals received from said cable; a handset; a first voice frequency low-pass filter connected between said handset and said modulator for bandlimiting voice signals received from said handset; and a second voice frequency low-pass filter connected between the output of said demodulator and said handset for filtering voice signals transmitted from said demodulator to said handset.

Claim 13

A telephone set for use with other like sets in a local frequency division multiplexed telephone system for connection to public telephone lines, the telephone set comprising: a connection for connecting said telephone set into said local system; a pilot tone receiver for detecting a pilot tone signal received at said connection and for supplying a local reference signal in accordance therewith; a carrier signal generator responsive to a clock signal for developing a carrier signal having a frequency that is a sub-multiple of the frequency of said clock signal, and responsive to said local reference signal so that said carrier signal is in phase synchronism with said received pilot tone signal; a handset; a modulator coupled to said handset and to said connection for modulating voice signals from said handset onto said carrier signal and applying said modulated carrier signal to said connection; and a demodulator coupled to said connection, to said handset, and to said carrier signal generator for demodulating signals received at said connection in phase sychronism with said received pilot tone signal.

Claim 14

A telephone set for use with other like sets in a local frequency division multiplexed telephone system for connection to public telephone lines, the telephone set comprising: a connection for connecting said telephone set into said local system; a pilot tone receiver for detecting a pilot tone signal received at said connection and for supplying a local reference signal in accordance therewith; a carrier signal generator responsive to a clock signal for developing a carrier signal having a frequency that is a sub-multiple of the frequency of said clock signal, and responsive to said local reference signal so that said carrier signal is in phase synchronism with said received pilot tone signal; a handset; a modulator coupled to said handset and to said connection for modulating voice signals from said handset onto said carrier signal and applying said modulated carrier signal to said connection; and a demodulator coupled to said connection, to said handset, and to said carrier signal generator for demodulating signals received at said connection in phase sychronism with said received pilot tone signal.

Claim 15

The telephone set of claim 9, additionally comprising a phase delay coupled between the output of said carrier signal generator and said demodulator for phase-delaying said carrier signal an amount corresponding to the phase delay experienced by a signal propagating through said local telephone system.

Claim 16

The telephone set of claim 10, additionally comprising a mode selector coupled to said carrier generator for setting the frequency of said carrier signal.

Claim 17

The telephone set of claim 9, additionally comprising a voice frequency low-pass filter connected between said handset and said modulator for bandlimiting voice signals from said handset.

Claim 18

A telephone set for use with other like sets in a local frequency division multiplexed telephone system for connection to public telephone lines, the telephone set comprising: a connection for connecting aid telephone set into said system; a phase detector coupled to said connection for detecting the phase of a pilot tone signal received at said connection; a clock for producing a clock signal having a clock frequency; a carrier generator connected to said clock for dividing said clock signal to produce a carrier signal having a frequency that is a sub-multiple of said clock frequency; a modulator coupled to the output of said carrier generator for modulating a voice signal onto said carrier signal; a voltage-controlled oscillator connecting said carrier generator to said phase detector so that said carrier signal developed by said carrier generator is in phase synchronism with said received pilot tone signal; a phase delay coupled to the output of said carrier generator for phase-delaying said carrier signal an amount corresponding to the phase delay experienced by a signal propagating in the system; and a demodulator coupled to said connection and to the output of said phase delay for demodulating a signal received at said connection.

Claim 19

A telephone set for use with other like sets in a local frequency division multiplexed telephone system for connection to public telephone lines, the telephone set comprising: a connection for connecting aid telephone set into said system; a phase detector coupled to said connection for detecting the phase of a pilot tone signal received at said connection; a clock for producing a clock signal having a clock frequency; a carrier generator connected to said clock for dividing said clock signal to produce a carrier signal having a frequency that is a sub-multiple of said clock frequency; a modulator coupled to the output of said carrier generator for modulating a voice signal onto said carrier signal; a voltage-controlled oscillator connecting said carrier generator to said phase detector so that said carrier signal developed by said carrier generator is in phase synchronism with said received pilot tone signal; a phase delay coupled to the output of said carrier generator for phase-delaying said carrier signal an amount corresponding to the phase delay experienced by a signal propagating in the system; and a demodulator coupled to said connection and to the output of said phase delay for demodulating a signal received at said connection.

Claim 20

The telephone set of claim 13, additionally comprising: a handset; a first voice frequency low-pass filter connected between said handset and said modulator for bandlimiting voice signals received from said handset; and a second voice frequency low-pass filter connected between the output of said demodulator and sand handset for filtering voice signals transmitted from said demodulator to said handset.

Claim 21

The telephone set of claim 14, additionally comprising a pilot signal bandpass filter coupled between said connection and said phase detector for passing said pilot tone signal.

Claim 22

The telephone set of claim 13 additionally comprising carrier frequency selection means connected to said carrier signal generator for setting the frequency of said carrier signal.