Antenna input circuit for radio receiver
First Claim
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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Abstract
A low-impedance loop antenna for receiving medium-frequency-band radio waves has an inductance of 1 microhenry up to 100 microhenries and an effective loop area larger than 20 cm2, whereby it is capable of receiving radio waves with a markedly improved rejection of undersirable radiations in the form of electric field from external noise sources. Such low-impendance loop antenna is coupled to a radio receiver via an input transformer whereat the impedance of this antenna is stepped up for the purpose of impedance matching. The input transformer has a primary winding provided with a tap adapted to be connected to the antenna and whose ends are connected to a variable capacitor constituting a tuning circuit jointly with the input transformer.
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Citations
13 Claims
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1. An antenna input circuit for a radio receiver, comprising:
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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. - View Dependent Claims (2, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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3. An antenna input circuit for a radio receiver, comprising:
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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; and 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 with a center wire and a shield sheath, respectively, of a coaxial cable 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 lead and another lead connected to said third antenna terminal; a second capacitor and an inductor arranged in parallel between said fourth antenna terminal and ground, said inductor having substantially the same inductance as that of said low-impedance loop antenna, said second capacitor substantially grounding said fourth antenna terminal for very-high-frequency-band signals but serving substantially as an impedance to medium-frequency-band signals; 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. - View Dependent Claims (4)
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Specification