Patent GB-642738-A (GB)
Title: Improvements in automatic code selectors
IPC: H04L15/26
Filed: 1947-07-15
Abstract: 642,738. Electric selective signalling. McGOFFIN, W. W. July 15, 1947, No. 18820. [A Specification was laid open to inspection under Sect. 91 of the Acts, July 15, 1947.] [Class 40 (i)] A bell-operating circuit which responds only to the call sign of a radio station comprises a uniselector with two banks S1, S2 associated respectively with a mark-timing relay 50 and a space-timing relay 85 in such a way that the switch, which advances one step for each marking element of the call sign, is restored to normal as soon as a mark or space is received that does not conform to the call sign. The association of the timing relay with the banks S1 and S2 is adjustable by means of manually set switches so that the device can be set for any call sign within the capacity of the uniselector. Received impulses are repeated by relay 41 to the reverse drive stepping magnet 45 and to relays 50, 85 which are slow to operate and slow to release respectively. If the signal received is a dot, the switch steps on and the relay 50 is disconnected before it can pull up. If it should have been a dash, relay 82 also will be energized over wiper S1 and locked temporarily by 85, and, in consequence, the relapse of the impulse relay energizes the resetting magnet 68 which restores the uniselectors to normal. If a dash is correctly received, the operation of the timing relay 50 releases 82 to prevent the operation of 68. If a dash is received when the apparatus is set for a dot, the timing relay 50 energizes the resetting magnet via wiper S1. In all cases, the space-timing relay 85 begins to de-energize at the end of the impulse. If the space is of inter-element length, 41 re-energizes 85 before it has time to fall. If the space should have been longer, the resetting magnet is energized by the impulse relay over wiper S2. When a long space is correctly received, the relapse of 85 energizes 90 which remains locked during the ensuing pulse to prevent the operation of the resetting magnet by the impulse relay. On the relapse of 85 after the selector reaches a predetermined position, the alarm circuit is completed. If, however, signals continue to come in, the resetting magnet is operated and the alarm circuit is disconnected. The resetting magnet when operated by a faulty marking signal or a short space locks until the relapse of the space-timing relay. Bank S2 of the uniselector is provided with neutral contacts so that any timing between pulsations will be accepted since no potential is fed to resetter feed arm 77. This neutral position may also be used to run two letters together. In a modification the apparatus is made automatically responsive to the desired signal irrespective of the time settings of relays 50 and 85. In the case of relay 50 resistor 72 which normally discharges the condenser after each pulsation is made of very high value so that condenser S1 is not fully discharged and closes more quickly on the arrival of the next pulse. In the case of relay 85 a resistor is connected in series with a condenser across the coil so that the condenser is not immediately fully charged. Release of pulsing relay 41 shortcircuits the resistor so that relay 85 is held operated for a time proportional to charging time.