GB767109A - Transmitting apparatus - Google Patents

Abstract

767,109. Fire and like alarm systems. KENGELBACH, W. Nov. 16, 1953 [Nov. 15, 1952], No. 31732/53. Drawings to Specification. Class 118 (1). In an alarm system there are provided a plurality of radio transmitters with means for modulating each with a respectively distinctive audio-frequency signal, and a central receiving station comprising means for demodulating the received signals which are then applied to one or more resonant relays responsive to the modulating frequency or frequencies employed, the arrangement being such that on receipt of any one distinctive audio-frequency signal, the relay or relays actuate apparatus, whereby a distinctive indication of the transmitter from which the signal is being received is given. In a first embodiment each transmitter comprises a spring-loaded disc which on being rotated and released causes a reed to vibrate, thereby developing an audio-frequency signal used to modulate the transmitter. The reeds at all of the transmitters have the same resonant frequency, the transmitters being distinguished by the number of times the disc is rotated and released. In a second embodiment the manually-operated disc is coupled to a further disc having a plurality of projections, the reed being vibrated a corresponding number of times when the disc is rotated and released. The manually-operated disc may be coupled to more than one such further disc, the latter discs effecting the transmission of respective groups of different audio-frequency wavetrains, one group corresponding to a units digit, the second to a tens digit and so on, whereby the transmission may be identified. At the receiver, a resonant relay comprising a plurality of reeds tuned to the audio-frequencies employed is provided, the excitation of any one reed actuating a corresponding stepping switch, the final positions of the stepping switches being shown by a lamp panel which consequently indicates the transmitter from which the transmission was received. The receiver is also provided with an audible alarm which sounds whenever a signal is received. In addition, means may be provided for permitting radio telephonic communication between each transmitter and the central receiver.