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Fish finder capable of discriminating sizes of fish

  • US 4,081,783 A
  • Filed: 09/22/1976
  • Issued: 03/28/1978
  • Est. Priority Date: 09/26/1975
  • Status: Expired due to Term
First Claim
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1. A fish finder capable of discriminating the sizes of fish, comprising:

  • a single transducer capable of transmitting and receiving high- and low-frequency ultrasonic sound waves simultaneously, one of said high- and low-frequency ultrasonic sound waves being emitted with a wide beam angle while the other of said waves is emitted with a narrow beam angle;

    receivers for processing the high- and low-frequency echo signals received by said transducer,a subtractor circuit for subtracting the received echo signal corresponding to the narrow beam angle from the received echo signal corresponding to the wide beam angle, anda recorder for recording the output from said subtractor circuit comprising echo signals corresponding to images of fish of desired size.

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