Patent GB-621724-A (GB)
Title: System for transmitting telegraph signals
IPC: H04L25/493
Filed: 1938-10-12
Abstract: 621,724. Telegraphy; copying telegraphy. HUDEC, E. Oct. 12, 1938, Nos. 29508, 29509, 29510, and 29511. Convention dates, Jan. 4, 1938, July 9, 1938, July 11, 1938, and Aug. 3, 1938. Addition to 621,723. [Classes 40 (iii) and 40 (viii)] The parent Specification discloses a method of transmitting telegraph signals by changing them into short pulses of constant amplitude and duration occurring at the beginning of each signal, transmitting these pulses, and at the receiver reconstituting the telegraph signals from the received pulses and locally-generated pulses. The present invention consists in synchronizing the locally-generated pulses by adjusting their phase. Multiplex telegraphy.-A standard oscillator 1, Fig. 9, feeds a subharmonic generator 2 to produce control pulses in 3 and drive the motor of a distributer 4; the signals picked up by the distributer from six tapes are combined at 6 with the pulses from 3 to produce pulses occurring at the beginning of each telegraph signal as described in the parent Specification, and these pulses are modulated on to a linecarrier from harmonic oscillator 5 and passed to the transmitter, where they are demodulated at 7 and keyed on to a radio-carrier at 8. The received pulses are demodulated at 16 and converted into the original telegraph signals at 17 for application to a distributer 19 feeding six tapes; the conversion is made as described in the parent Specification with the aid of control pulses developed at 14 from an oscillator 13 fed through a phase shifter 12 from a standard oscillator 11. In the receiver, the control pulses are applied to a phase comparator 18, where their phase is compared with a synchronizing pulse developed at the transmitter by extra contacts on the distributer 4; any phase difference is caused to actuate the motor of the phase shifter 12 to shift the phase of the receiver control pulses to synchronize with the received synchronizing pulses. Phase shifter.-A voltage uo, Fig. 1, is applied to a valve whose output circuit comprises condensers C and ganged variable resistances R, so that as R varies, the phase of voltage u2 varies from 0-180 degrees as compared with uo. A similar circuit has an output u, which can thus vary in phase as compared with uo by 0-360 degrees. The four resistances R are preferably as shown in Fig. 3, and are varied by a motor M. Phase comparison.-The synchronizing signal consists of a space and a mark invariably produced by two extra segments on the distributer at the transmitter. There are two corresponding segments on the receiver distributer, which thus receive the space and mark as reformed in the receiver. If the transmitted pulses lead the receiver control pulses, the mark signal begins before the first extra segment has been completely wiped and is applied to valve 1, Fig. 4, to charge condenser C, according to the extent of phase difference, to control valve 2 and motor M to adjust the phase shifter; the condenser is discharged by a distributor contact S preceding the first synchronizing contact. If the transmitted pulses lag behind the receiver control pulses, the mark does not commence until the second synchronizing contact has begun to be wiped, and is applied to a circuit similar to Fig. 4, but so as to make valve 1 non- conducting, so that condenser C is charged to a value corresponding to the lag. In a modification, the synchronizing signal consists of one pulse transmitted by one extra segment only on the transmitter distributer. A corresponding segment at the receiver connects terminals 3 and 5, Fig. 6, thus applying the received synchronizing signal from terminals 8, 9 and the locallygenerated signals from terminals 12, 13, in opposite polarity to discharge device K2. If the locally-generated pulse leads the received pulse, K2 ceases to conduct and V3 conducts to actuate the motor to adjust the phase-shifter. In a further modification, the receiver develops two sets of control pulses, differing only in their duration. The short control pulses cooperate with a lagging synchronizing pulse as described for Fig. 6, to produce a phase shift, and the longer control pulses co-operate with a leading synchronizing pulse to produce a phase shift; in this latter case, the discharge device K2 is ignited by the synchronizing pulse and made non-conductive by the control pulse, Figs. 7 and 8 (not shown). Picture telegraphy.-The telegraph signals may represent the light and shade of elemental areas.