| 摘要 |
PURPOSE:To allow an AM receiver which has only a PLL control part for MW to receive an LW wave, by supplying the output of the PLL control part to an LW local oscillating circuit, generating an S curve on the basis of the output of an intermediate frequency amplifying cirucit, and then performing AFC operation. CONSTITUTION:When the MW band is selected with a band changeover switch 24, an MW loxal oscillating circuit 1 is controlled by a PLL part 3 and its output fM is inputted to a mixing cirucit 14 to perform normal PLL reception. Then when the LW band is selected with a switch 25, an LW power voltage LW+B is applied to an LW local oscillating circuit 2 and a transistor (TR) 33 turns on to supply the output fL of the oscillating circuit 2 to the mixing circuit 14. At the same time, since a TR34 is in operation through a +B power source, the PLL part 3 also operates to apply the output of the low-pass filter 7 of the PLL part 3 rhrough a buffer amplifier 20 to the oscillating circuit 2, and the signal from an S curve signal generating circuit 17 is also applied through a resistance adding circuit 23, thereby performing AGC operation. |
