APPARATUS FOR UTILIZING AN A.C. POWER LINE TO COUPLE A REMOTE TERMINAL TO A CENTRAL COMPUTER IN A COMMUNICATION SYSTEM

• US 3,876,984 A
• Filed: 04/19/1974
• Issued: 04/08/1975
• Est. Priority Date: 04/19/1974
• Status: Expired due to Term

• Current Assignee: Allan Chertok
• Original Assignee: Allan Chertok
• Inventors: Chertok, Allan
• Primary Examiner(s): Pitts, Harold I.
• Application Number:
  US05/462,323
• Time in Patent Office: 354 Days
• Field of Search: 340/152,151,152R,163,310,149A 179/2DP
• US Class Current: 379/93.07
• CPC Class Codes: G06F 13/4063 Device-to-bus coupling
• CPC Class Codes: H04B 2203/5408 using protocols
• CPC Class Codes: H04B 2203/5416 by adding signals to the wave form of the power source
• CPC Class Codes: H04B 2203/5437 Wired telephone
• CPC Class Codes: H04B 2203/545 Audio/video application, e.g. interphone
• CPC Class Codes: H04B 2203/5483 using coupling circuits
• CPC Class Codes: H04B 2203/5491 using filtering and bypassing
• CPC Class Codes: H04B 3/542 the information being in digital form

Abstract

A system for interfacing a telephone party line extending from a central computer with a number of remote inquiry terminals. The system includes an a.c. power line disposed between the party line and the remote inquiry terminals, a line buffer modem (modulator/demodulator) connected between the party line and the power line, and a plurality of terminal modems each being associated with a one of the remote inquiry terminals and connected between the power line and the respective remote inquiry terminal. The communication signals received from a telephone party line are applied to the line modem connected to that line and transformed to a suitable form for transmission over an a.c. power line. The signals are then applied to the power line. The remote terminal modems transform the signal received from the power line back to suitable form for receipt by its associated remote terminal. Similarly, signals from the various remote terminals are transformed by the associated terminal modems to a form suitable for transmission and then transmitted over the a.c. power line to the line modem, where they are again transformed into signals suitable for retransmission over the telephone party line to a central computer.

Claims

1. In a system for communicating between a central computer and a plurality of remote inquiry terminals having a communication data channel connecting said central computer and a distribution substation, and a telephone party line coupled between said substation and said plurality of remote inquiry terminals, wherein an alternating current power line for transmission of electrical power at frequency f.sub.0, is located adjacent to at least one of said remote inquiry terminals, the improvement comprising:

a means for utilizing said alternating current power line for coupling one or more of said remote inquiry terminals to said telephone party line, said means for utilizing said alternating current power line comprising;

a party line modem including;

a party line coupling means for coupling signals from said party line to said line modem and from said line modem to said party line, a controlled oscillator generating a carrier signal nominally at a frequency f.sub.1, f.sub.1 being substantially different from the frequency f.sub.0 of the current on said alternating current power line, said oscillator, providing as an output said carrier signal at frequency f.sub.1 as modulated by signals received through said party line coupler from said party line, a power line coupling means coupling said party line modem to said power line, said power line coupling means only passing signals substantially at frequency f.sub.1 from said modem to said power line and only passing signals substantially at a frequency f.sub.2 from said power line to said party line modem, wherein frequency f.sub.2 differs substantially from frequency f.sub.1 and from the power transmission frequency f.sub.0 of said alternating current power line, said power line coupling means isolating said party line modem from the power current on said alternating current power line, a demodulator connected to said power line coupling means for demodulating said modulated signals substantially at frequency f.sub.2 and for providing output baseband signals, the output of said demodulator being connected to said party line coupler for providing transmission of said output baseband signals from said demodulator on said party line; and

at least one terminal modem associated with one of said remote inquiry terminals, said terminal modem including;

a terminal coupling means for coupling signals from said terminal modem to the associated one of said inquiry terminals and from the associated one of said inquiry terminals to said terminal modem, a controlled oscillator for generating a carrier signal nominally at said frequency f.sub.2, and connected to said terminal coupling means, said oscillator providing as an output signal said carrier signal nominally at frequency f.sub.2 as modulated by signals transmitted from said associated inquiry terminal through said terminal coupling means, a power line coupling means coupling said terminal modem to said power line, said power line coupling means passing only said signals substantially at frequency f.sub.2 from said terminal modem to said power line and passing only signals substantially at frequency f.sub.1 from said power line to said terminal modem, said power line coupling means isolating said terminal modem from the power current at frequency f.sub.0 on said alternating current power line, a demodulator coupled to said power line coupling means for demodulating said modulated signals substantially at frequency f.sub.1 and for providing output baseband signals, the output of said demodulator being coupled through said terminal coupling means to the associated one of said inquiry terminals.

2. The improvement in accordance with claim 1 wherein at the commencement of a transmission cycle from any one of said plurality of remote inquiry terminals, a transmit control signal is produced at said inquiry terminal permitting the oscillator in the associated terminal modem to produce as an output signal a carrier signal substantially at frequency f.sub.2, and wherein said party line modem includes detector means responsive to the receipt of said carrier signal substantially at frequency f.sub.2 to disable the oscillator in said party line modem for the duration of the transmission cycle from the transmitting inquiry terminal.

3. An apparatus in accordance with claim 2 wherein normally said sub-station produces and applies a line status signal to said party line, and wherein said sub-station removes said line status signal from said party line for periods, each period commencing at the receipt at said sub-station of the initial transmission from any one of said remote inquiry terminals and terminating following the application by said sub-station of a reply signal from said computer to said inquiring terminal on said party line, the improvement comprising means in all of said remote inquiry terminals for preventing all terminals except the inquiry terminal from transmitting signals on or receiving signals from said party line whenever said line status signal is removed.

4. An improvement in accordance with claim 2 wherein said party line modem includes a switching means between said demodulator and said party line coupling means, said switching means being in a position connecting the output of said demodulator to said party line coupling means upon receipt and detection of said carrier signal substantially at frequency f.sub.2 at said detector means, and being in a position disconnecting said demodulator output from said party line coupler otherwise.

5. An improvement in accordance with claim 1 including in said party line modem signal enhancing means connected between said power line coupling means and said demodulator means for enhancing signals substantially at frequency f.sub.2 and suppressing signals substantially at frequency f.sub.1.

6. An improvement in accordance with claim 1 wherein said means for coupling said party line modem to said power line comprises a hybrid coupling circuit.

7. An improvement in accordance with claim 1 wherein said party line modem oscillator and said terminal modem oscillator are frequency modulators.