Title: Remote underwater device activating system

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Abstract: An apparatus for activating a remote underwater device comprising detecting means responsive to incident acoustic waves provides signal indication of the presence or absence of predetermined frequencies thereof. A logic arrangement decodes only those signal indications indicating a joint presence of some of the pre-selected frequencies and the absence of others of the pre-selected frequencies. This discriminates signals against broad-band acoustic noise. The logic arrangement further includes means for activating the remote underwater device only if the decoded successive signal indications match a predetermined pattern. This further discriminates between a present received acoustic wave and a prior transmitted acoustic wave present because of multipath or reverberation. Lastly, a timing and gating means responsive to a first decoded signal indication couples the detecting means to the logic arrangement only at periodic intervals thereafter. The time gating also reduces the chances of obtaining a prior multipath and reverberation signal because the pulse repetition period of the successive acoustic waves is predetermined.


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