GB1403251A - Communication system - Google Patents

Abstract

1403251 Digital transmission over power lines; party line systems CENTURY INTERNATIONAL CO Ltd 24 July 1972 34547/72 Headings H4P and H4R Grouped message stations are connected to a hierarchical network in the form of a pyramid, which may be an electric power distribution system, messages being routed by means of an address defining the series of control stations through which a message must pass in order to reach its destination. Messages destined for a message station connected to the same control station pass directly, but other messages are temporarily stored at a control station until polled by a higher control station. Each control station A1 contains an interrogating transmitter 12 which polls lower stations in turn by means of addresses stored at 16. Each control station, as well as message stations, also contains an interrogation receiver 18. When the appropriate address is received a circuit 20 ml opens gate 24 ml allowing messages in store 26 to flow through transmitter 28 ml into receiver 30 cl in control station A1 and parallel stations. Interrogation and message frequencies are different. At each interrogation circuit at control stations, received addresses are compared; if the control station is not to accept a message for retransmission a gate 36 1 is blocked. However if the message is for retransmission to a higher level, gate 36 1 is opened permitting passage to store 38. If store 38 becomes full or after each lower station has been polled, further polls are inhibited and gate 173 is opened allowing any messages in 44 received from station B1 to pass through transmitter 28 cl. Data flow to lower and higher stations are substantially independent of each other and may take place simultaneously. When used in conjunction with an electric power system, distribution transformers may be by-passed by a repeater as shown in Fig. 9. Signals f3, f 4 in one direction may be collected by transformer winding 203 and passed by series resonant circuits 210, 211 through amplifiers 214, 215, another pair of resonant circuits 212, 213 and another winding 201 to the outgoing line. A non-physical gap 216, 217 comprising a radio, optical, or acoustic link must be provided for electrical isolation. For providing amplification along an unbroken line, in a three phase system (see Fig. 1a, not shown) signals collected from one line may be retransmitted on another line to avoid interference. Alternatively in a single phase system where cyclic transposition is not possible, the frequency ranges may be changed at successive amplification points to avoid interference through feedback (see Fig. 11b, not shown).