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Receiver for audible alarm

  • US 4,617,555 A
  • Filed: 04/17/1985
  • Issued: 10/14/1986
  • Est. Priority Date: 04/17/1985
  • Status: Expired due to Fees
First Claim
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1. Apparatus to detect sonic signals within a predetermined range of frequencies comprising an electret microphone with integral FET impedance converter for receiving the sonic signal, band-pass filter means connected to the output of said electret microphone, AGC means connected to the output of said filter means and producing an AGC bias voltage which is applied to the FET to control the sensitivity of said electret microphone, and means connected to the output of said filter means for producing a defined response to the presence of the sonic signal.

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