Patent GB-819753-A (GB)
Title: Telephonic concentration arrangements
IPC: H04Q3/52
Filed: 1957-02-26
Abstract: 819,753. Automatic exchange systems. MARZIN, C., CHAPPEY, M., and LUCAS, P. Feb. 26, 1957 [Feb. 29, 1956], No. 6392/57. Class 40 (4). In an automatic satellite (non-exchange) each of the ten subscribers of the satellite is identified by a combination of two frequencies out of five, which identification signal is transmitted over all free exchange lines between the satellite and the main exchange by a coder at the satellite when a subscriber calls, or by a coder at the exchange when his line is wanted. Receipt at the exchange of a subscriber's identification signal effects operation of a gate to connect the exchange appearance of that subscriber to a free exchange line selected by equipment at the exchange, and the transmission over that exchange line of a single frequency different from those used for subscriber identification which frequency identifies the exchange line. At the satellite the reception of this single frequency on the exchange line opens a gate connecting that exchange line to a common receiver for the subscriber's identification frequencies, which receiver responds to the subscriber's identification signal received to connect the relevant subscriber to that exchange line. Conventions employed for representing trigger circuits and gates.-In the drawings trigger circuits are idicated by rectangles, for bi-stable circuits the rectangle is divided by a full line and for mono-stable circuits by a dashed line. The rest state of a trigger circuit is indicated by that half of the rectangle in which the reference character appears, bi-stable circuits being changed-over by a signal on the lead terminating in that half, and restored by one on the lead terminating in the other half. Gate circuits are indicated. by circles and have references differing by a multiple of 100 from the reference of the trigger circuit controlling them. A gate circuit which is open in the rest condition of the associated trigger circuit has a barred reference, e.g. 114j (Fig. 1) is open in the rest condition of trigger circuit 14j. A gate circuit controlled jointly by two trigger circuits is indicated by a product reference, e.g. gate 212j x 212m is open when trigger circuits 12j and 12m are both in their rest conditions. Satellite subscriber initiates a call.-When subscriber I lifts his handset a negative pulse passes via gate 212j x 212m (Fig. 1) and the connection 151 to the coder 16. Assuming both exchange lines J and M to be free (gates 114j and 114m both open) an identification signal consisting of the two frequencies f and f 2 indicative of subscriber I is transmitted over both exchange lines. At the exchange (Fig. 2) there is a priority trigger circuit 19 which allots the exchange lines in turn (if free) and it is assumed that line J has been allotted, both exchange lines being free. The identification signal f1, f2 passes through the open gates 424j and 424m to the decoder 23 which in response thereto applies a pulse to its common output 231 and to that lead of 187.1 to 187.10 corresponding to the relevant subscriber. The former pulse passes via gates 219 and 124j to operate the line designating trigger circuit 24j, which in turn operates the mono-stable line selecting trigger circuit 18j associated with exchange line J, whereupon gate 118j is opened and the frequency fj of that exchange line is applied to the exchange line J. At the satellite this frequency passes via gate 214j and filter 13j to operate the line selecting trigger 14j which opens gates 314j and 414j. The subscriber's identification signal f1, f 2 then passes via gate 414j to the decoder 29 which in response thereto applies a pulse via lead 87.1 and gate 314j to operate the line access trigger circuit 12j of the calling subscriber. Gate 112j is thus opened and the calling station is connected to the selected exchange line J. Meantime, at the exchange the pulse applied by decoder 23 to lead 187.1 passes through gate 324j to operate the line access trigger circuit 22j. Gate 122j is thus opened and the exchange line J is connected to the exchange appearance of the calling subscriber. On receipt of dialling tone the caller dials the wanted number, each break of the dial opening the gate 125 so that a burst of oscillations of frequency f N  passes via gate 312j to the exchange line J and thence via the gate 524j and filter 46j to an amplifier detector 47j. The arrangement is such that the subscriber's loop circuit to the exchange is completed when 22j is energized and 47j is in the unoperated condition, this being effected by gate 322j x 147j (Fig. 2). Fig. 3 shows the detector 47j and gate 322j x 147j in more detail. The signal f N  is applied to the input terminal of 47j and changes the voltage at the collector of transistor 93 from a negative value to a positive one. With 22j at rest the emitter of transistor 96 (constituting the gate 322j x 147j) is at -10 volts and relay 97 is not energized. When 22j is triggered this emitter rises to zero volts and 97 operates to close the loop, provided that<SP> </SP>fN is not being received. Relay 97 then repeats the dial pulses to the exchange by relapsing as each burst of f N  is received. The call is completed by the exchange equipment in the usual manner, the satellite equipment not being concerned in these operations. All exchange lines busy.-In this event circuits 14j, 14m, 24j and 24m are all energized so that both gates 114j and 114m are closed, preventing access by the caller to either exchange line. The calling subscriber is notified of this condition by the absence of dial tone. Satellite subscriber called.-When the subscriber I is wanted, the selection by the exchange of his line 61 (Fig. 2) applies ground to the test conductor thus producing a pulse at the output of the differentiating circuit 71 which passes via gate 922j x 922m (line idle) to the coder 20. This coder in response to the pulse on lead 115.1 sends the signal f1, f2 via one or both of gates 624j and 624m provided one or both are open. This signal has the same effect at the exchange as it did when generated at the satellite in the case of subscriber I calling. An exchange line, say J, is selected and fj is applied thereto; the subscriber's line access trigger circuit 22j is operated and gate 122j is opened. At the satellite the receipt of f1, f2 and fj triggers 14j and 12j and gate 112j is opened. Triggering of 12j also opens the gate 312j causing application to exchange line J of the loop frequency f n  so that the loop circuit to the exchange remains open until the reply of the called party stops the transmission of f N  by closing the gate 125, whereupon relay 97 operates to close the loop. All exchange lines busy.-The gate 724j x 724m (Fig. 2) is open and a busy signal is applied by the generator V to the busy conductors of all the lines 61 to 70 energizing all the busy signal relays (not shown) so that the caller receives busy tone. Release.-When the satellite subscriber connected to line J hangs up, his gate circuit 125 is again opened and f N  is transmitted to the exchange where relay 97 opens the loop to the exchange. The consequent removal, by the exchange, of ground from the test conductor produces a pulse of opposite polarity from differentiating circuit 71 which passes via gate 222j to restore 24j, and via 824j to restore 22j and operate 21j. The last-named circuit causes the restoration frequency F to be applied via gate 121j to the exchange line J. At the satellite this signal F passes via gate 514j and filter 76j to restore the trigger circuits 14j and 12j.