CHIRP SIGNAL APPARATUS

• US 3,835,446 A
• Filed: 11/25/1966
• Issued: 09/10/1974
• Est. Priority Date: 11/25/1966
• Status: Expired due to Term

• Current Assignee: Richard Rowlands
• Original Assignee: Richard Rowlands
• Inventors: Rowlands, Richard
• Primary Examiner(s): Farley, Richard A.
• Application Number:
  US05/597,835
• Time in Patent Office: 2,846 Days
• Field of Search: 340/3,3FM 343/17.2PC 333/71 329/199
• US Class Current: 367/135
• CPC Class Codes: G01S 15/104 wherein the transmitted pulses use a frequency- or phase-modulated carrier wave
• CPC Class Codes: Y10S 367/901 Noise or unwanted signal reduction in nonseismic receiving system

Abstract

The apparatus disclosed herein includes a hydrophone for sensing underwater sonar signals, a gain controlled amplifier receiving the hydrophone output, and a chirp signal detector for detecting chirp signals having an instaneous frequency which increases with time. The chirp detector is further described as including a specially clamped reed which is electromagnetically driven into vibration having an instantaneous frequency equivalent to that of the sensed chirp signal and having an instantaneous peak amplitude corresponding to a characteristic nonlinear frequency vibration amplitude response. The apparatus disclosed further includes threshold detector means responsive to reed vibration amplitude for indicating the reception of the chirp signal to utilization apparatus.

Claims

1. Chirp signal responsive apparatus comprising:

first means providing a first electrical output signal representative of a chirp signal whose frequency increases with time;

second means connected to said first means for receiving said first electrical output signal and producing in response thereto a magnetic field of corresponding frequency;

clamping means;

a resilient reed having one end clamped by said clamping means and having a free end positioned in said field for vibration;

third means positioned intermediate the clamped and free ends of said reed and spaced from the rest position of said reed a distance to limit the excursion of a portion of the reed along its length during vibration and to increase the instantaneous resonant frequency of said reed; and

fourth means positioned adjacent the free end of said reed for providing a second electrical output signal which varies as a function of the amplitude of vibration of said free end.

2. Apparatus according to claim 1 wherein said first means includes:

means for limiting the amplitude of said first electrical output signal.

3. Apparatus according to claim 2 further comprising:

fifth means connected to said fourth means for receiving said second electrical output signal and for producing an indication signal in response to said second electrical output signal exceeding a threshold level.

4. Apparatus according to claim 1 further comprising:

fifth means connected to said fourth means for receiving said second electrical output signal and for producing an indication signal in response to said second electrical output signal exceeding a threshold level.

5. Apparatus according to claim 1 wherein said third means comprises:

support means; and

a screw adjustably threaded therethrough having an end thereof positioned adjacent said reed intermediate its free and clamped ends.

6. Apparatus according to claim 1 wherein said third means further comprises:

support means extending from said clamping means; and

a plurality of screws adjustably threaded through said support means each having an end thereof positioned and respective distance intermediate said clamped and free ends of said reed, the end of one said screw positioned further from said clamped end of said reed being laterally separated from said reed at rest a greater distance than is the end of another said screw positioned closer to said clamped end of said reed.

7. Apparatus according to claim 6 wherein said first means includes:

means for limiting the amplitude of said first electrical output signal.

8. Apparatus according to claim 1 wherein said third means comprises:

a projection extending from said clamping means in the direction of said free end of said reed and having a reed excursion limiting surface extending from said clamped end of said reed, portions of said surface positioned progressively further from said clamped end being separated progressively greater distances from said reed at rest.

9. Apparatus according to claim 1 wherein said third means further comprises:

a pair of projections extending from said clamping means in the direction of said free end of said reed on respective sides of said reed and having identical opposed, convexly shaped reed excursion limiting surfaces flaring away from said clamped end.

10. Apparatus according to claim 9 wherein said first means includes:

means for limiting the amplitude of said first electrical output signal.

11. Apparatus responsive to an electrical chirp signal of frequency varying in time in a predetermined manner comprising:

drive means responsive to an input signal for producing a magnetic field;

reed means positioned in said fiEld for vibrating in response thereto;

resonant frequency modifying means positioned adjacent to said reed means for modifying the instantaneous resonant frequency of said reed only when a predetermined amplitude of reed vibration is exceeded; and

detector means adjacent to said reed means for producing an electrical signal indicative of the amplitude of reed vibration.

12. Apparatus according to claim 11 wherein:

said reed means includes a vibratable reed having a resonant frequency and clamped at one end; and

said resonant frequency modifying means includes surface means spaced a predetermined distance from a rest position of said reed for engagement with a medial portion of said reed when said reed is excited into vibration at its resonant frequency, said surface means being formed for causing an instantaneous decrease in the effective length of the free end of said reed when engaged by said reed during vibration.