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Antenna input circuit for radio receiver

  • US 4,278,980 A
  • Filed: 03/28/1979
  • Issued: 07/14/1981
  • Est. Priority Date: 03/30/1978
  • Status: Expired due to Term
First Claim
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1. An antenna input circuit for a radio receiver, comprising:

  • a first input transformer including a primary winding and a secondary winding, said primary winding having a grounded first end lead, a second end lead, and a tap lead;

    a first capacitor connected across said first and second end leads to form a tuning circuit jointly with said primary winding;

    a first antenna terminal connected to said tap lead of said primary winding;

    a grounded second antenna terminal, said first and second antenna terminals being adapted to be connected with respective output leads of a low-impedance loop antenna having an inductance of 1 microhenry up to 100 microhenries for reception of medium-frequency-band radio waves;

    a third and a fourth antenna terminal adapted to be connected to respective wires of a twin-lead type feeder extending from an antenna for receiving very-high-frequency-band radio waves;

    a second input transformer including a primary winding and a secondary winding for very-high-frequency-band radio signal reception, said primary winding having a grounded center tap lead, a first end lead connected to said third antenna terminal and a second end lead connected to said fourth antenna terminal through a second capacitor which substantially prevents the passage therethrough of medium-frequency-band signals but passes very-high-frequency-band signals therethrough;

    an inductor between said fouth antenna terminal and ground, and having substantially the same inductance as that of said low-impedance loop antenna; and

    short-circuiting means for short-circuiting said first and fourth antenna terminals when reception of medium-frequency-band radio waves is intended without the connection of said low-impedance loop antenna but with the connection of said very-high-frequency-band radio wave receiving antenna.

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