Patent GB-686707-A (GB)
Title: A system for signalling between two stations
IPC: H04B1/54
Filed: 1950-07-19
Abstract: 686,707. Electric selective signalling systems. SVENSKA AKTIEBOLAGET GASACCUMULATOR. July 19, 1950 [July 21, 1949], No. 18026/50. Class 40 (i) [Also in Group XL(c)] A system whereby a shore station can control the operation of a fog-horn, radio beacon &c, at an unattended station is continuously supervized with the aid of a step-by-step timing switch at each station. These switches are reciprocally controlled so as normally to maintain synchronism, which can be disturbed at appropriate points in the cycle by the suppression of synchronizing impulses to give controlling effects, and is also disturbed by fault conditions to give characteristic signals at the shore stations. Synchronous operation of switches. Switch 2-6 in the beacon stations (Fig. 1) is constantly driven by an impulse generating arrangement 1 except when the follower of cam 3 is in the depressions. In these positions, a radio receiver 7 is connected up. Similarly, switch 32-36 (Fig. 2) in the shore station is continuously driven by a device 31 except for brief periods,' determined by cam 33, when a radio receiver 37 is in operation. The normal timing is such that when the receiver at one station is connected up, a cam 6 or 36 at the other connects up a radio transmitter (not shown). The resulting response of the receiver energizes a relay 15 or 45 which makes a driving circuit alternative to that interrupted by cam 3 or 33 so that stepping is at once resumed. Control by shore station. To exercise control, the operator disconnects the transmitter at an appropriate point in the cycle. In consequence, the next time cam 3 at the beacon station opens the driving circuit, no alternative circuit is made by receiving relay 15, and slow-to-release relay 20, which is normally energized in parallel with the driving circuit, falls back and energizes the driving magnet 9 of a further step-by-step switch 8-13. Relay 20 also makes an alternative driving circuit for 1, reoperates and is then held over contacts operated by cam 3. Stepping of switch 2-6 then continues until these contacts again change over, whereupon driving magnet 9 receives a further impulse and (say) a fog horn is energized over springs controlled by cam 13. Cam 11 now changes over its contacts so that magnet 9 receives no further impulses from relay 20 until the radio transmitter at the shore station has been reconnected. The next time thereafter that the receiver 7 is connected up, receiver relay 15 re-operates and a circuit is made via its front contact for magnet 9, which steps switch 8-13. The next radio impulse causes a further step after which cam springs 11-13 change over, the fog horn is cut off, and normal stepping is resumed. An alternative control is exercised by disconnecting the radio transmitter at a point in the cycle at which a switch, not shown, but connected to points II is operative instead of switch 8-13. Tell-tale signals sent back from beacon station; faults. When the timing switch at the beacon station is stepped by relay 20 instead of by the receiving relay 15, the closure of the circuit of the radio transmitter by cam 6 occurs somewhat late and as a result relay 50 at the shore station. which is normally held by the receiving relay 45 when cam contacts 33 change-over, has time to fall back and give an impulse to stepping magnet 39 of a switch 38-43. When the cam springs 33 are restored, automatic stepping is resumed and when they change-over again 50 again has time to fall back to give another step to switch 38-43, which thereupon closes an indicating circuit over springs 43. The switch remains in this condition until the shore transmitter is reconnected, when relay 45 is energized before 50 falls back to complete a circuit for magnet 39 through contacts on cam discs 41, 42, 35 to step switch 41-43. The next radio impulse causes a further step after which cam springs 41-43 change-over, and the conditions are back to normal. Other changes of condition, e.g. faults, in the beacon by means not shown cause the impulse rate of device 1 to be accelerated or retarded, by altering the RC values in a saw-tooth voltage generating circuit. When they are retarded both half-cycles. are affected and a circuit is made by cam springs 43. in switches I and II, as previously described for the tell-tale signal to operate both the fog horn and (say) a radio beacon. In this case, however, the radio pulses are so long delayed that a relay 55 which is sluggish enough to remain energized during the periods of relapse of 50 in the previously described case, falls back and operates an audible alarm which can be replaced by a visible signal by operating a manual switch, thus indicating a change in the rate of operation of the beacon stepping switch 1. The shore stepping switch rate of operation may now be manually varied to coincide again with that at the beacon station, and the change required will indicate the nature of the fault at the latter.