Patent GB-647773-A (GB)
Title: Telecommunication exchange
IPC: H04Q3/52
Filed: 1947-03-07
Abstract: 647,773. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Federal Telecommunication Laboratories, Inc.). March 7, 1947, No. 6462. [A Specification was laid open to inspection under Sect. 91 of the Acts, Sept. 15, 1947.] [Class 40 (iv)] [Also in Group XL (a)] An automatic exchange system incorporates an electronic sequence switch. When the calling party lifts his handset 10 kc. pulses so produced in the distributer 2 seize a line-finder as described in Specification 645,871 which opens the gate 41. Dialled impulses passed thereby are demodulated, each impulse then operating the flip-flop pair 61, 62 to transmit pulses to the tens and units gates 93, 106. The former of these is biassed by the electronic sequence switch 90 in its home position, to pass the pulses to condenser 82b and the charge so built up deflects the beam of the register 91 on to the particular electrode 78b representing the first digit. Valves 96, 97 change over during each impulse train, at end of which their restoration causes a pulse 103 to be delivered to condenser 82a to step the sequence switch 90. With the latter in its second position 106 is biassed to transmit the units digit to set the register 92. As described, the exchange comprises 20 lines, the tens digits taking values 1 . . . 4 and the units digits 1 ... 5. The beam of distributer 110 rotates continuously at 10 kc., 4 dynodes being swept per revolution, so providing to the gate 121 a pulse 118 of a duration which embraces all the time positions of the lines in the particular tens group registered on switch 91. The beam of distributer 111 rotates at 50 kc. and feeds pulses 122 to the gate 121 at the time positions of all lines having the particular units digit registered on switch 92. Gate 121 produces pulses only when pulses 118, 122 coincide, i.e. at the 'time position of the called line. If the called line is idle then switch 90 is stepped from its third to its fourth position by a pulse from 129. If, however, the called line is busy, coincidence of pulses incoming from the distributer with those obtained from gate 121 changes over valves 138, 139 to block valve 129 and prevent 90 from stepping. In the fourth position of 90 valves 141, 142 are unblocked, the former transmitting ringing current to the called line via the output gate 43. When the called subscriber answers 138, 139 change over as described above to step switch 90 to its fifth position by a pulse from 142. Speech then ensues as described in Specification 645,871. When the called subscriber hangs up a positive pulse emitted from valve 37 on release of the line-finder causes release tubes 158 ... 160 to discharge condenser 82a ... 82c to return the beams of switches 90 . . . 92 to their home positions. Switch construction. The electronic switches 90 ... 92 each comprise the usual cathode 70, focusing arrangements 72 ... 74 and a pair of deflecting plates 75, 76. The beam may fall on any one of a number of dynodes 78, the secondary emission from which is collected by the anode 80. The beam before impinging on a dynode passes through a corresponding slot in a metal screen 77 which is connected as shown in Fig. 7 to the condenser 82 which provides the deflection voltage. After this condenser has received the desired charge, this leaks away until the edge of the beam reaches the edge of a slot whereupon the screen collects enough electrons from the beam to stabilize the charge on 82 and consequently the beam.