| 摘要 |
PURPOSE:To obtain the 2nd IF output signal which is highly stable by detecting the difference of a fundamental oscillating frequency of the 2nd local oscillating circuit and an oscillating frequency of the 1st local oscillating circuit to control the 1st local oscillating frequency by a PLL circuit. CONSTITUTION:A multiplier 9 doubles a frequency of an oscillator 10. In receiving a CATV signal of 50-450MHz, when the 1st IF signal frequency is 600MHz, the 1st local oscillating frequency is 650-1,050MHz and when the 2nd IF signal frequency is 62MHz, the oscillating frequency of the local oscillator 10 is 331MHz. The difference between the 1st local oscillating frequency and the oscillating frequency of the oscillator 10 is 319-719MHz by a mixer 11, which attains the frequency division by a fixed frequency divider 12 and the control of the oscillating frequency of the 1st local oscillating circuit 3 via the PLL circuit 13. |
