| 摘要 |
PURPOSE:To enable to receive FM, by switching tuning coils for television and FM, provided for the antenna input circuit, interstage circuit and local oscillation circuit by means of switching diodes. CONSTITUTION:At the high-channel reception, a switching voltage at around +15 volts is fed to a high-band power supply terminal VH. At the input circuit 2, winding is made at high-band coils 8 and 18 through the turning-on of switching diodes 11 and 9. At the interstage circuit 4, since switching diodes 46, 47 are on, the band of 4.5MHz required for the television band is taken with coils 39 and 40. At FM reception, terminals VH and VL are both taken as about -15 volts. In the circuit 2, diodes 11, 14, 19, 22 are all off and also in the local oscillation circuit 5, diodes 66 and 69 are off. In the circuit 4, the turning-off of diodes 46, 47 56, 57 makes lost the damping operation by resistances 54, 55. Thus, a sharp characteristic of 1.5MHz can be obtained between the coils of the circuit 4. |
