GB526239A - Improvements in and relating to wireless receiving apparatus - Google Patents

Abstract

526,239. Electromagnetic relays. FLETCHER, H. L. Feb. 8, 1939, No. 4194. [Class 38 (v)] [Also in Group XL] Wireless receiving apparatus of the kind adapted, on receipt of a predetermined carrierfrequency signal, to actuate an alarm device or perform a similar operation, comprises a detector 4 of the non-energy consuming type having an input circuit 1, 2 tunable to the carrier frequency and, associated with its output circuit a relay 10 arranged, on receipt of the signal to open and close periodically a circuit containing a local voltage source 7, said relay being operated by energy derived from the received signal, the arrangement being such that energy released from the local source at each closure of the circuit is stored in a device which after a predetermined time causes an alarm 14 or like device to operate. The relay 10 is of the vibration galvanometer type, the moving coil 10 being mounted on a phosphor bronze or like strip so as to be free to vibrate between the poles of a permanent magnet, the natural period of vibration of the coil being adjustable by varying the tension of the strip. The strip carries a moving contact 11 which is arranged to make and break with a fixed contact 12 twice during each cycle of vibration of the coil. Each time the contacts close, a relay 13 shunted by a condenser 15-is energized, and after a predetermined interval, during which the condenser is charging up, the relay 13 closes its contacts and the device 14 is energized. The apparatus is effective when the carrier frequency applied to the input circuit 1, 2 is modulated by a continuous audiofrequency as the natural frequency of vibration of the coil 10. In a modification, Fig. 2, the relay 10 moves a contact 18 into the field of a permanent . magnet 19, where the contact is held against a fixed contact 20 until it is released, after a predetermined interval, by the energization of a winding 23 through a delayed-action relay 22. Closure of the contacts 18, 20 energizes the relay 22 and also a thermal relay 21 which, after an interval, closes the circuit of the alarm 14, In a further modification, Fig. 3 (not shown), the energization of the relay 10 closes a maintaining circuit for the relay and also energizes a delayed-action relay which, after an interval, first operates the alarm device and then opens the maintaining circuit. Specification 526,230, [Group XL], is referred to.