Remote underwater device activating system

• US 3,939,465 A
• Filed: 06/15/1970
• Issued: 02/17/1976
• Est. Priority Date: 05/14/1969
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Walsh, George M., Alarie, Allan P., Helton, Robert A.
• Primary Examiner(s): Farley, Richard A.
• Application Number:
  US05/048,891
• Time in Patent Office: 2,073 Days
• Field of Search: 340/5 R, 340/16 C, 340/3 FM, 340/15, 340/171 A, 340/171 PF, 343/5 SA, 343/225, 325/28, 325/30, 325/33, 325/37, 325/47, 325/65
• US Class Current: 367/133
• CPC Class Codes: H04B 11/00 Transmission systems employing sonic, ultrasonic or infrasonic waves
• CPC Class Codes: H04L 27/26 Systems using multi-frequency codes H04L27/32 takes precedence
• CPC Class Codes: Y10S 367/901 Noise or unwanted signal reduction in nonseismic receiving system

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.

Claims

1. Apparatus for activating a submerged device, the apparatus comprising:

detecting means responsive to incident acoustic waves which communicate a succession of signal pulses for detecting said signal pulses to provide signal indications of the presence or absence of predetermined frequencies therein;

a logic arrangement coupled to said detecting means for the coding only those signal indications manifesting a joint presence of certain preselected frequencies and the absence of other preselected frequencies, said logic arrangement further including means responsive to successive decoded signal indications, said logic arrangement including a delay means and a gate responsive to said delay means to permit activation of said submerged device only if a second one of said signal indications occurs a predetermined time after the occurence of a first one of said signal indications; and

said detecting means further comprising a first wideband filter for passing a first of said present preselected frequencies and a second wide band filter for passing a second of said present preselected frequencies, and a first and a second limiting means coupled respectively to said first wide-band filter and said second wide-band filter, the output of said first limiting means being coupled to a pair of band-pass filters tuned to a pair of said preselected frequencies, said second limiting means being coupled to a second pair of band-pass filters tuned to a second pair of frequencies of said preselected frequencies.

2. Apparatus for activating a submerged device, the apparatus comprising:

detecting means responsive to incident acoustic waves for detecting successive pulse signals communicated by said waves, said detecting means including;

a low pass and a high pass band width channel, and limiting means within each channel for normalizing various varying input signal levels so as to provide a constant output level signal;

a first plurality of narrow band-pass filters responsive to the low-pass band normalizing means output signal for providing signal indication of the presence of corresponding preselected frequencies such as f_A and f_B ;

a second plurality of narrow band-pass filters responsive to the high-pass band normalizing means output signal for providing signal indication of the presence of other preselected frequencies such as f_C and f_D, where f_A <

f_B <

f_C <

f_D ;

a logic arrangement for detecting only those signal indications manifesting the joint presence of preselected ones of the frequencies such as f_A and f_D and the absence of other preselected frequencies such as f_B and f_C, said logic arrangement further including means responsive to successive decoded signals for activating the submerged device only if the decoded successive signals match a predetermined pattern, said activating means including delay means and gating means responsive to a first of said signal indications for gating a second of said signal indications only if said second signal indication occurs at a predetermined time after the occurence of said first signal indication.

3. A system for activating a remote underwater device comprising:

a transmitter for generating acoustic waves which communicate a succession of signal pulses, said waves having predetermined frequencies therein;

detecting means responsive to incident ones of said generated acoustic waves for detecting said signal pulses to provide signal indications of the presence or absence of predetermined frequencies therein;

a logic arrangement for decoding only those signal indications manifesting a joint presence of m out of n preselected frequencies and the absence of n-m other preselected frequencies, said logic arrangement further including delay means and gating means responsive to a first of said signal indications for gating a second of said signal indications only if said second signal indication occurs a predetermined time after said first signal indication for activating said remote underwater device; and

said detecting means comprising a first and a second band pass filter for passing respectively a first portion and a second portion of said predetermined spectrum, a first and a second limiting means coupled to output terminals of respectively said first and said second band pass filters, one of said present frequencies passing through said first band pass filter and a second of said present frequencies passing through said second band pass filter.

4. In combination:

means for generating a sequence of signal pulses, having a predetermined spectrum in which certain predetermined frequencies are present and in which other predetermined frequencies are absent;

means responsive to said sequence of signal pulses for detecting the presence and absence of said predetermined frequencies of said spectrum and providing a first signal indicating such presence and such absence of said frequencies;

means responsive to said first signal of said detecting means for providing a second signal at a predetermined time subsequent to said first signal;

means responsive to the temporal concurrence of said second signal with said first signal in response to a subsequent one of said sequence of said signal pulses, for providing a signal indicating the simultaneous presence of said second signal and said subsequent first signal of said detecting means; and

said detecting means comprising a first and a second band-pass filter for passing respectively a first portion and a second portion of said predetermined spectrum, a first and a second limiting means coupled to output terminals of respectively said first and said second band-pass filters, one of said present frequencies passing through said first band-pass filter and a second of said present frequencies passing through said second band-pass filter.

5. A secure communication system comprising:

means for radiating pulse train signals into a medium, said pulse train signals having a predetermined frequency spectrum in which a plurality of predetermined frequencies are present and which a plurality of predetermined frequencies are absent;

means spaced from said radiating means in said medium for receiving said pulse train signals;

means fed by said receiving means and responsive to said pulse train signals for decoding said pulse train signals, said decoding means having logic means responsive to the relative spectral positions of said present frequencies and said absent frequencies in said spectrum for providing a signal, if, and only if, there is an absence of each of said absent frequencies and if, and only if, there is a presence of each of said present frequencies; and

said receiving means comprises a first and a second band-pass filter for passing the frequencies respectively in a first portion and in a second portion of said spectrum, and a first and a second limiting means coupled respectively to first and said second band-pass filters, the output of said limiting means being coupled to filters tuned to individual ones of the frequencies of said spectrum.