Patent GB-388625-A (GB)
Title: Improvements in or relating to telegraph systems with repetition of the signals
IPC: H04B1/10
Filed: 1932-06-09
Abstract: 388,625. Wireless signalling; synchronism indicators. BAKKER, A., 207, Theresiastrasse, The Hague, and DUUREN, H. C. A. VAN, 18, Heerenweg, Noordwijkerhout, both in Holland.-(Assignees of Netherlands of the Hague, State of the, Holland.) June 9, 1932, No. 16301. Convention date, June 11, 1931. [Classes 40 (iii) and 40 (v).] In a telegraph system which involves repetition of the signals to eliminate the effects of extraneous disturbances, means are provided at the receiver to convert the effect of missing signals into the same effect as that due to added signals. In one embodiment, Figs. 1 and 2, audio-frequency generators 41, 43 produce modulating frequencies for marking and spacing respectively, which are directed through transformer 45 by the transmitting relay 9, to a radio transmitter. At the receiver, the low frequency currents pass to two filters 47, 54, the former excluding the spacing frequency and the latter passing all frequencies. These filters are followed by rectifiers 48, 55 and relays 50, 57 respectively, which are both energized by the rectifiers when no signals are being received, their moving contacts 51, 58 contacting with contacts 52, 60 respectively. The contact 51 is connected to the receiving relay and when a marking signal is received through filter 47 it moves to the negative marking contact 53. When a spacing signal is received through filter 54, contact 51 receives positive spacing potential from contacts 52, 58, 59 due to the actuation of contact 58 of relay 57. Additional signals due to atmospherics &c. cause the actuation of both relays 50, 57 resulting in a marking impulse from contact 53 to contact 51, while fading &c. results also in a marking impulse, the two relay contacts being in the position shown and connected to negative marking contact 60. As an alternative contact 58 may control the biasing of one of the valves of the rectifier 48'. In a multiplex system comprising two channels, Figs. 3 and 4, four audio-frequency generators 66, 75, 69, 72 are used to produce signals corresponding to the four possible combinations' of marking and spacing positions for the two channels, each channel having a pair of relays 61, 62 and 63, 64, wired in series or parallel, which according to their position select the output from one of the generators to pass through transformer 77 and filter 78 to the radio transmitter. At the receiver, two radio receivers are used to mitigate fading effects, each receiving one side band of the carrier wave, their low frequency parts co-operating in the same way with rectifiers 79, 80, 81 as described hereinafter with reference to one of them, 46. The low frequency currents pass to filters 48, arranged in such a way that the frequency n<1> of generator 66 influences the rectifier 79, the frequency n<2> of the generator 75 influences the rectifiers 79, 80, and the frequency n<3> of the generator 69 influences the rectifier 80. All the frequencies n<1> .. n<4> influence the rectifier 81 through filter 54. Since except when fading occurs, rectifier 81 is always impulsed, relay 57 in its output circuit connects positive spacing potential to the left-hand contacts of receiving relays 50a, 50b. When fading occurs, however, the receiving relays have negative marking potentials on both fixed contacts. The repetition of the signals may be effected by a Baudot type of multiple distributer, Fig. 5, which in the example illustrated is arranged for four transmissions of the same signal. The segments are divided into four groups 1 .. 4 each containing five segments, and synchronizing segments 100, 101 are provided. The contact device 5 of the signal transmitter comprises five contacts, one of which is shown connected through relay 8 to a segment 7 of group 4 and supplying it with positive spacing potential. The wiper 6 on reaching segment 7 connects transmitting relay 9, and energizes relay 8 which connects the corresponding segment 11 of group 3 through relay 12 to spacing potential. The wiper 6 on its second revolution, on reaching segment 11 repeats the signal on relay 9 and connects segment 14 of group 2 through relay 15 to spacing potential. The wiper 6 on its third revolution, on reaching segment 14 repeats the signal on relay 9 and connects segment 17 of group 1 to spacing .potential. On its fourth revolution the wiper 6 on reaching segment 17 energizes relay 9 with spacing potential causing the fourth transmission of the signal element. At the receiver the synchronously rotating receiving distributer has a similarly arranged set of repeating relays 21, 24, 27 and a recording relay 30, the righthand contacts of the former being all connected to the moving contact of the receiving relay 18 which is connected to marking or spacing potential in accordance with the incoming signals. If one of the repeating relays has once had spacing current, each of the others receives spacing current and also the recording relay 30, and only if no spacing signals are received by relay 18, does the recording relay 30 receive marking potential. This eliminates the effect of stray marking potentials introduced either by atmospherics or fading effects converted into marking effects by the apparatus previously described. A transmitter and a receiver repeating system may be coupled to a common drive and extra channels may be added by modifying the distributers. A startstop system after slight modification, Fig. 7 (not shown), may be used to follow the output relays at the receiver and operate a receiver magnet and if necessary a retransmitter. An extension of the system for operating two repeating systems per revolution of the distributer with one transmitting and one receiving apparatus, Fig. 8 (not shown), is also described. In order to maintain synchronism which would ordinarily be adversely affected by long continued fading, the transmitting and receiving devices at each end are jointly coupled to the same drive and on each revolution transmit correction impulses in both directions. An automatic warning may be given when the correction relay is repeatedly energized owing to interference and a signal may be produced so that the transmitter or receiver is automatically stopped, depending on which end is being disturbed. The Specification as open to inspection under Sect. 91 comprises also a modification of the arrangements shown in Fig. 2, for use if marking waves only are transmitted. The signal may influence a relay such as 50 and a relay such as 57 may be fed from a second radio receiver tuned to an adjacent wavelength and serve to connect the marking contact of relay 50 to spacing voltage when atmospherics &c. occur. The subsequent apparatus is then designed to counteract the effect of missing signals only. This subject-matter does not appear in the Specification as accepted.