Patent GB-648375-A (GB)
Title: Telecommunication system
IPC: H04Q11/04
Filed: 1947-02-07
Abstract: 648,375. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Federal Telephone & Radio Corporation.). Feb. 7, 1947, No. 3707. [A Specification was laid open to inspection under Sect. 91 of the Acts, Aug. 8, 1947.] [Class 40 (iv)] [Also in Groups XL (a) and XL (c)] In an automatic exchange system of the electronic distributer type, the time positions of the subscriber's lines in the scanning cycle are designated by two dialled digits. Each digit effects a proportional radial displacement of a rotating beam which is thereby caused to pass through one of several arcuate slots in a screen whose angular positions correspond to the time positions of the dialled digits. Two such beams, for the tens and units digits respectively, are used to determine the required time position and produce a gating pulse thereat. The system is described with reference to a 20-line exchange in which the tens digits may have values 1 ... 5 and the units digits 1 ... 4. When the calling subscriber lifts his handset, battery is applied to corresponding electrodes of the input and output distributer tubes 5, 6 to cause secondary emission current to flow when the beam impinges thereon. 10 kc. pulses so produced seize a line-finder which opens the gate 47 to pass pulses modulated by dial impulses to the impulsing circuit, Fig. 4, where demodulation takes place and the impulses are transmitted by the tens dial gate 71 to set the binary counter 100 ... 103. Valves 82, 83 change over during the impulse train at the end of which they restore causing 85 to send a pulse to change over 76, 77. This blocks the tens dial gate 71 and opens the units dial gate 72 by biassing the screen grid, thereby passing the units digit to the binary counter 104 . . . 107, 114. At the end of this train-another pulse from 85 restores 76, 77, thereby changing over 78, 79 to block both 71 and 72 on their suppressor grids and to enable valve 89 in the speech circuit. A pulse from 78 also changes over 91, 92 to open the ringing gate 93 so passing ringing current from the oscillator 94 to the output gate 49. In the respective register circuits, valves 119, 120 and 109, 112, 116 conduct or not according to the condition of the corresponding pair of registering valves, and are arranged to draw anode current proportional to the power of 2 that the pair represents. The deflecting potentials on electrodes 137, 237 depend on the respective total anode currents in resistors 121, 122 and hence on the digit dialled. In the tube 230 the beam rotates at 50 kc. and an interposed slotted screen (not shown) allows the beam to fall on the dynode 243, and so deliver a pulse to the grid 131 of tube 130, only at the time positions corresponding to all lines having the dialled units digit. Likewise the deflection potentials are such as would cause the beam' of tube 130, rotating at 10 kc., to sweep the dynode 143 for the period corresponding to the time positions having the dialled tens digit. During this period the units pulse is received by the grid 131 so that the anode 138 emits a pulse to 146 at the time position of the called line. This pulse is applied to valve 148 and when pulses coinciding with these are produced on wire 149 due to the called subscriber answering, this valve conducts to change over valves 91, 92 thus blocking the ringing gate 93. Conversation then takes place via input gates 47, 48 and output gates 49, 50; gates 47 and 50 being opend by pulses from the line-finder and 48, 49 by pulses from 146 in the register. Pulses derived from the register and also fed via valve 152 to wire 25 in opposition to incoming pulses 23 produced when the called subscriber answers to prevent these pulses seizing another linefinder. When the calling subscriber hangs up the line-finder disengages, causing 158 to produce a restoring pulse for the register and for the valves 76 ... 79. Electronic switch construction. The tube comprises the usual electron gun structure and horizontal and vertical plates for rotary scanning. The beam passes through the gap between the central electrode 137, Fig. 6, and a toroidal-shaped electrode 136, the radius of the sweep being varied by the potentials thereon. The screen 138 is provided with arcuate slots 139 ... 142. Fig. 5, having different angular positions so that the beam impinges on the dynode 143 during a period of the scanning cycle dependent on the radius of the sweep. A separate anode 144 may be provided to collect secondary emission from the dynode or the screen 138 may be used for this purpose.