Patent GB-213654-A (GB)
Title: Improvements relating to means for synchronising the movements of two rotating bodies
IPC: H04N1/36
Filed: 1922-12-30
Abstract: 213,654. Stephenson, W. S., and Walton, G. W. Dec. 30, 1922. Thermionic modulating systems; copying telegraplas. - Moving bodies at a transmitting station and a receiving station are synchronized, e.g. for purposes of picture transmission or television, by modulating the electromagnetic waves emitted by a wireless or wired-wireless transmitter by an alternating current of a low-frequency dependent on the movement at the transmitting station, and using such modulation to set up an alternating current of the same frequency to maintain the movement at the receiving station. Fig. 1 shows one transmission arrangement. The shaft 7 of the transmission drum is driven by a directcurrent shunt motor 8, 9 serving as a rotary converter to supply low-frequency alternating current to the primary winding of a transformer 6 of which the secondary winding is in the gridcircuit of a valve 1 with a reaction coupling 2, 3, and this valve generates continuous oscillations, controlling oscillations in a power valve 4, which are impressed on the aerial system 5. The grid circuit of the valve 1 includes a high-resistance or leak 70 across which is connected a battery 71 supplying direct current to the grid circuit upon each closure at 72 of contacts on the transmission drum. In a modification, the shaft 7 is driven by a synchronous motor supplied from alternating current mains, the motor being in parallel with the primary winding of the transformer 6, and two valves contributing alternate half-waves to the continuous wave are each in circuit with onehalf of the secondary winding. Fig. 3 shows a receiving arrangement comprising a reaction coupling 16, 17 and a valve 15 with an oscillatory circuit 18, 19 tuned for filtering out the low-frequency of the modulation. The arrangement may include several stages of thermionic valve amplifications. The low-frequency impulses in the plate circuit pass through the condenser 20 and a polarized relay 21, causing the tongue 26 of this relay to oscillate at that frequency and allowing direct current from the mains 29, 30 to pass alternately in opposite directions through the inductance 32 which with a condenser 33 forms an oscillatory circuit tuned to the frequency. A secondary winding 35 coupled to the inductance 32 is in circuit with the alternating current synchronous motor 36 driving the receiving drum. The intermittent direct current impulses for the picture transmission pass through the inductance 18 to a relay 23 controlling the source of light 24 for the reproduction. Fig. 4 shows a modified receiving arrangement in which the relay 21, Fig. 3, is in circuit with a secondary winding 48 of a transformer of which the primary winding 38 with a condenser 37 is in one branch of the plate circuit of the valve 15, and ancther secondary winding 39 with a condenser 40 and a resistance 41 is in a second branch. The direct current impulses for the picture transmission are in this case taken from the plate circuit of a second valve 44 of which the grid is connected to the mid-point of the resistance 41 and the filament 43 is connected to a junction 42 of the windings 38, 39. In another receiving arrangement enabling the use of local power at the receiving station as the main source of power, thus avoiding a large degree of amplification, alternating current of a frequency slightly different from that of the moduation is supplied to the primary winding of a transformer from an alternator driven by a motor supplied by direct current mains, or from a rotary converter supplied from the mains on the direct-current side. The secondary winding of the transformer is in the plate circuit of the valve 15, and a current of a frequency midway between the two low-frequencies in this circuit is obtained from this circuit by the use of a transformer and is supplied to a svnchronous motor. The shaft to be synchronized is driven from the shaft of the alternator through differential gearing of which the carrier for the planet pinions is secured to the shaft of the synchronous motor. In a further modification, enabling the use of a local main source of power, the shaft of a synchronous motor driven by alternating current of the frequency of the modulation carries the armature of a direct current motor and local direct current mains supply the field of the synchronous motor and supply also the field and armature of the direct-current motor in series. The tendency of the direct current motor to run slightly faster than the synchronous motor is counteracted by the tendency of the latter to remain in synchronism. According to the Provisional Specification, the mains 29, 30, Fig. 3, may be connected between the tongue 26 and the mid-point of the inductance 32, each end of this inductance being connected to one of the contacts of the relay 21, and being connected also to the mid-point through a condenser.