Am-fm radio receiver having novel rf input circuit

Claim 2

An AM-FM radio receiver comprising; a high-frequency amplifying circuit for amplifying received signals in both the AM and FM frequency bands; signal transmission means including a first signal channel comprising first impedance means having a high impedance for frequencies in the AM band for permitting an FM high-frequency signal to pass therethrough, and a second signal channel comprising a second impedance means having a high impedance for frequencies in the FM band for permitting an AM high-frequency signal to pass therethrough, said first or second signal channels being selected without switching therebetween when an FM or AM signal appears at the output of said high-frequency amplifying circuit; a frequency mixing circuit connected to said high-frequency amplifying circuit through said signal transmission means so as to receive an output signal from said high-frequency amplifying circuit selectively passing through said first and second signal channels in case of FM reception and AM reception respectively; means for applying an output signal of an FM local oscillation circuit having a first oscillator to the input of said frequency mixing circuit; means for applying an output signal of an AM local oscillation circuit having a second oscillator to the input of said frequency mixing circuit; and means for selectively actuating said FM local oscillation circuit and AM local oscillation circuit in case of FM reception and AM reception respectively.

Claim 3

An AM-FM radio receiver according to claim 1, wherein said signal transmission means consists of an FM tuning circuit connected to the output of said high-frequency amplifying circuit, an FM intermediate frequency trap circuit connected to the input of said frequency mixing circuit and a coupling capacitor connecting said two circuits with each other, and transmits high-frequency signals through said coupling capacitor in case of FM reception and through a coil constituting said FM tUning circuit and a coil constituting said FM intermediate frequency trap circuit in case of AM reception.

Claim 4

An AM-FM radio receiver according to claim 1, wherein said signal transmission means consists of a coil connected to the output of said high-frequency amplifying circuit, variable capacitors connected in parallel with said coil and constituting an FM tuning circuit together with said coil, a coil connected to the input of said frequency mixing circuit, a capacitor constituting an FM intermediate frequency trap circuit, which is connected to series with both last said coil and said coil constituting said FM tuning circuit, and a capacitor connected between the output of said high-frequency amplifying circuit and the input of said frequency mixing circuit, said coil and variable capacitor constituting said FM tuning circuit functioning as a load for FM high-frequency signals in case of FM reception, said capacitor constituting said FM intermediate frequency trap circuit functioning as a load for AM high-frequency signals in case of AM reception.

Claim 5

An AM-FM radio receiver according to claim 1, wherein the output of said high-frequency amplifying circuit is connected to the input of said frequency mixing circuit through a capacitor and connected to an oscillation coil constituting said AM local oscillation circuit through a coil constituting an FM tuning circuit and a severally provided resistor, and a junction point between said oscillation coil and said resistor and a junction point between an AM intermediate transformer and an FM intermediate transformer which are connected to the output of said frequency converting circuit are connected respectively to the FM terminal and the AM terminal of an AM-FM change-over switch the neutral terminal of which is grounded.

Claim 6

An AM-FM radio receiver according to claim 1, wherein said high-frequency amplifying circuit consists of a field effect transistor, an AM-FM change-over switch, the neutral terminal of said switch being connected to the gate of said transistor, the FM terminal and AM terminal of said switch are connected to one end of a step-up coil and an AM tuning circuit respectively, and a capacitor connected between an intermediate tap of said step-up coil and an antenna, which resonates at a frequency near a received signal frequency together with said step-up coil.

Claim 7

An AM-FM radio receiver wherein a coil and a variable capacitor which constitute an FM tuning circuit are connected to the output of a high-frequency amplifying circuit for amplifying both signals of the AM and FM frequency bands, said FM tuning circuit functioning as a load in case of FM reception, an FM high-frequency signal which appears across the terminals of said FM tuning circuit is applied to the input of a following frequency converting circuit together with an output of an FM local oscillation circuit so that a frequency converting is carried out, while an intermediate frequency trap circuit which is connected to the input of said frequency converting circuit and resonates at an FM intermediate frequency consists of a coil and a capacitor of low capacitance, said capacitor is connected in series with said coil constituting said FM tuning circuit, a resistor connected between a junction point between said capacitor and said coil and the input side of an AM local oscillation circuit functions as a load in case of AM reception, an AM high-frequency signal which appears across the terminals of said resistor is applied to the input of said frequency converting circuit together with an output of said AM local oscillation circuit through said coil constituting said intermediate frequency trap circuit so that a frequency converting is carried out.

Claim 8

An AM-FM radio receiver wherein a coil and a variable capacitor which constitute an FM tuning circuit are connected to the output of a high-frequency amplifying circuit for amplifying both signals of the AM and FM frequency bands, said FM tuning circuit functioning as a load in case of FM reception, an FM high-frequency signal which appears across the terminals of said FM tuning circuit is applied to the input of a following frequency converting circuit together with an output of an FM local oscillation circuit so that a frequency converting is carried out, while an intermediate frequency trap circuit which is connected to the input of said frequency converting circuit and resonates at an FM intermediate frequency consists of a coil and a capacitor of low capacitance, said capacitor is connected in series with said coil constituting said FM tuning circuit, a resistor connected between a junction point between said capacitor and said coil and the input side of an AM local oscillation circuit functions as a load in case of AM reception, an AM high-frequency signal which appears across the terminals of said resistor is applied to the input of said frequency converting circuit together with an output of said AM local oscillation circuit through said coil constituting said intermediate frequency trap circuit so that a frequency converting is carried out.

Claim 9

An AM-FM radio receiver comprising; an antenna circuit including an antenna; a high-frequency amplifying circuit for amplifying signals in both the AM and FM frequency bands received by said anteNna circuit; signal transmission means including a first signal channel for permitting an FM high-frequency signal to pass therethrough, and a second signal channel for permitting an AM high-frequency signal to pass therethrough; a frequency mixing circuit connected to said high-frequency amplifying circuit through said signal transmission means so as to receive an output signal of said high-frequency amplifying circuit selectively passing through said first and second signal channels in case of FM reception and AM reception respectively; means for feeding an output signal of an FM local oscillation circuit having a first oscillator to the input of said frequency mixing circuit; means for feeding an output signal of an AM local oscillation circuit having a second oscillator to the input of said frequency mixing circuit; means for selectively actuating said FM and AM local oscillating circuits in case of FM reception and AM reception respectively; a coil connected in series with said antenna, said coil being adapted to present a high impedance for a received signal in the FM frequency band and a relatively low impedance for a received signal in the AM frequency band respectively; and an AM-FM channel-over switch having first, second and third terminals, said first terminal being connected to the input of said high-frequency amplifying circuit through a capacitor constituting together with said coil a band-pass filter which allows a received signal in the FM frequency band to pass therethrough, said second terminal being connected to the output of said coil, said third terminal being connected directly to the input of said high-frequency amplifying circuit, said second terminal being adapted to be selectively connected to said first and third terminals in case of FM reception and AM reception respectively.

Claim 10

An AM-FM radio receiver comprising; an antenna circuit including an antenna; a high-frequency amplifying circuit for amplifying signals in both the AM and FM frequency bands received by said anteNna circuit; signal transmission means including a first signal channel for permitting an FM high-frequency signal to pass therethrough, and a second signal channel for permitting an AM high-frequency signal to pass therethrough; a frequency mixing circuit connected to said high-frequency amplifying circuit through said signal transmission means so as to receive an output signal of said high-frequency amplifying circuit selectively passing through said first and second signal channels in case of FM reception and AM reception respectively; means for feeding an output signal of an FM local oscillation circuit having a first oscillator to the input of said frequency mixing circuit; means for feeding an output signal of an AM local oscillation circuit having a second oscillator to the input of said frequency mixing circuit; means for selectively actuating said FM and AM local oscillating circuits in case of FM reception and AM reception respectively; a coil connected in series with said antenna, said coil being adapted to present a high impedance for a received signal in the FM frequency band and a relatively low impedance for a received signal in the AM frequency band respectively; and an AM-FM channel-over switch having first, second and third terminals, said first terminal being connected to the input of said high-frequency amplifying circuit through a capacitor constituting together with said coil a band-pass filter which allows a received signal in the FM frequency band to pass therethrough, said second terminal being connected to the output of said coil, said third terminal being connected directly to the input of said high-frequency amplifying circuit, said second terminal being adapted to be selectively connected to said first and third terminals in case of FM reception and AM reception respectively.