Patent GB-369713-A (GB)
Title: Improved devices for the automatic reception of wireless telegraphic signals
IPC: H04L15/26
Filed: 1931-02-03
Abstract: 369,713. Selectors responsive to code signals. ELFORD, E. N., Tudor Lodge, Dorney Reach, Taplow, Buckinghamshire. Feb. 3, 1931, No. 3410. [Class 40 (iv).] A selector responsive to a wireless telegraphic signal, such as dashes and spaces of four and one second duration respectively, comprises a rotary step-by-step switch, as used in telephony, operated by locally generated timed impulses, the contacts of which are so interconnected amongst themselves and to relays that the switch proceeds under the control of the required signal (with predetermined tolerances if desired) to a position in which an alarm is given, the switch being sent home without giving the alarm if the signal does not conform to requirements. On receipt of the first dash, relay AR in the anode circuit of the wireless receiver pulls up and operates clutch magnet C so that cam M is rotated from a shaft continuously rotated by an elective or clockwork motor, and impulses over springs X controlled by cam M are delivered once per second to switch magnet S. At the end of the dash, the switch is standing on contacts 4 and the relapse of AR during the space sends an impulse over wiper W3 to magnet S to drive the switch to contacts 5 while the timed pulse from X at the end of the space steps the switch to contacts 6. During the space (switch on contacts 4, 5) the circuit of clutch magnet C is maintained over wiper W1. The remaining dash-space-dash of the signal drives the switch in similar manner to contacts 16 and relay BR pulls up over W1, locks over re-set key R and closes an indicator circuit. Operation of key R releases BR and energizes SR which locks over W4 and com pletes a homing circuit for magnet S. Rejection of incorrect signals. If a space occurs whilst a dash should be coming in, relay SR pulls up over wiper W3 and back contacts of AR, and homes the switch. If a dash extends over a space period (no space impulse due to relapse of AR) SR receives a timed impulse from X over wiper W2 in position 4 or 10 of the switch which is thereupon homed. Relay BR is slow to operate so that it does not pull up over contact 16 when the switch is homed. Modifications. Instead of the back contacts of relay AR sending an impulse to magnet S during a space period, this relay closes an alternative circuit for S over the impulse springs X so that the switch is stepped at one second intervals during a space. The back contacts of AR also close the circuit of an additional relay which should then be operated during space periods. If a space period does not occur at the propel time this relay is not operated and a homing circuit for the switch is completed. If a dash extends into a space period, the release relay is operated as described with reference to Fig. 1. The connections to the switch contacts may be arranged so that the selector accepts a signal comprising an initial dash of not less than three seconds, subsequent dashes of not less than two seconds and spaces occurring in the 4th to 6th or 9th to 11th second, provided the errors are not cumulative. Instead of the cam being continuously driven during receipt of a signal it may be driven through a certain angle to close the impulse springs and open the circuit of the clutch magnet so that the cam is returned by a spring and the clutch re-engaged. The Provisional Specification also states that the timed impulses may be provided by a second step-by-step switch operated by constantfrequency A.C. which may be converted to halfwave unidirectional impulses by a rectifier.