Patent GB-670760-A (GB)
Title: Electrical synchronizing apparatus
IPC: H04L7/033
Filed: 1949-09-30
Abstract: 670,760. Automatic phase control systems. TELETYPE CORPORATION. Sept. 30, 1949 [Oct. 15, 1948], No. 25188/49. Class 38 (iv). Apparatus for synchronizing impulses derived from a local impulse source with received telegraph signal impulses comprises electronic means for comparing the phase of the locally produced impulses with that of the received signal impulses and deriving therefrom a potential which varies in polarity in dependence on whether the locally-produced impulses are fast or slow with respect to the received signal impulses, together with reactance means controlled by the said potential for automatically adjusting the phase of the locally-produced impulses so that synchronism is restored. Receiving apparatus.-As shown in Figs. 1, 2, and 3, a multiplex telegraph receiver as described in Specification 670,759, [Group XL (b)], comprises a crystal-controlled oscillator 12, for driving the receiving distributor, whose output is supplied to a frequency divider 13 of the type described in U.S. Patent No. 2,410,389. The frequency divider provides two frequencies at conductors 14, 16 which are connected to respective fixed contacts co-operating with a rotor 17 of a manually operated selector switch 18, which allows operation of the apparatus on two, three or four channels. The rotor 17 is connected to the grid of the left-hand portion of valve 21, and this portion is alternately conducting and non-conducting in accordance with the input. When non-conducting the increase in anode potential is applied via a biasing network 24 to the negatively-biased grid of the left-hand portion of a squaring amplifier valve 26, a square-wave output being derived in the anode circuit of the right hand portion over conductors 28, 29. As shown, the switch 18 is in the position for two-channel operation, but for four channels the conductor 28 is connected via a fixed contact and the rotor 31 and through a condenser 33 to the negatively-biased grid of the righthand portion of valve 21, a succession of negative pulses appearing at the output and being applied to the distributer 40 to cause it to operate to receive transmitted signals. For three channels the operation is the same but a different frequency is supplied from the divider 13. For two channels the conductor 29 supplies a square wave output via rotor 37 to a trigger circuit 39 whose output is taken via rotor 31 to the grid of the right-hand portion of valve 21 to provide pulses to operate the distributer. Synchronizing apparatus.-The output of the left hand triode of valve 21 is also applied to the negatively biased grid of the left hand triode of valve 43, whose anode is connected to the negatively biased grid of the right hand triode, square waves of opposite phase being produced in the two outputs over leads 48 and 54 respectively. Assuming the switch 51 is in position for four-channel reception, the conductor 48 is connected via rotor 49 to the negatively-biased grid of the right hand portion of a twin triode gate valve 53, and the conductor 54 is connected to the right hand portion of a similar gate valve 58, the right hand portions, when conducting, supplying blocking potentials to the respective left hand portions, which act as normal amplifiers when the right hand portions are not conducting. The received line signals are passed through a squaring amplifier, not shown, to the negatively-biased grids of a twin triode valve 62 so that each time a signal transition from " mark " to " space " occurs the left-hand portion conducts and a transition from " space " to " mark " causes the right hand portion to conduct to rapidly discharge the condenser 64 and produce sharp negative pulses on the conductor 63. The negative pulses are applied to the positively-biased grid of the left hand portion of a " one-shot " multivibrator 66, positive square-topped impulses being produced in its output for every signal transition, and the multi-vibrator then returning to its normal position. The positive impulses are applied over conductor 67 to the negatively biased grids of the left hand portions of the " fast " gate valve 53 and the " slow " gate valve 58. Since signals 180‹ out of phase are supplied to the grids of the right hand portions of valves 53, 58 one right hand portion will conduct when the other is non-conducting. If the left hand portion of valve 58 is conducting its output is applied to a phase inverter valve 72, whose output is applied to the negatively biased anode of the left hand portion of double diode 76. If the left hand portion of valve 53 is conducting the resulting fall in anode potential is applied to the positively biased cathode of the right hand portion of double diode 76. The cathode of the left hand portion and the anode of the right hand portion of valve 76 are connected to an averaging filter 83, no output appearing on conductor 87 when the outputs from the two diodes are equal, i.e. synchronizing is complete, and a positive or negative polarity appearing on conductor 87 when one or other predominates. The output on conductor 87 is fed to the negatively biased grid of a conventional reactance valve 88 so adjusted that a centre zero correction meter 90 in its anode circuit is at the zero position when no correction potential is being received from valve 76, the reactance tube being connected via conductor 91 to the grid circuit of oscillator 12 to apply correction and the amount of drift, fast or slow, being indicated by the meter. The trimmer 15 may be used for manual correction.