| 摘要 |
PURPOSE:To have the number of tuning voltage potentiometers of the 1st local oscillator, by shifting the oscillating frequcency of the 2nd local osicllator by the frequency difference of adjacent channels, and using a common oscillating frequency for each pair of adjacent channels of the 1st local oscillator, in a reception system of a CATV reception converter of a double conversion system. CONSTITUTION:At the reception of a channel 10, a changeover switch 21 is closed, a semi-fixed capacitor C is short-circuited, and an oscillation freqnecy fosc2 of the 2nd local oscillator 19 is 561.25 MHz. The oscillating frequency fosc1 of the 1st local oscillator 16 is 693.25 MHz and an output frequency 61.25 MHz is obtained to a reception frequency 193.25 MHz of the channel 10. At the reception of the channel 11, the switch 21 is opened and the semi-fixed capacitor C is lived. In this case, the oscillating frequency fosc2 of the 2nd local oscillator 19 is shifted to 567.25 MHz and the oscilating frequency fosc1 of the 1st local oscillator 16 remains 693.25 MHz, the output frequency 61.25 MHz is obtained to the reception frequency 199.25MHz. |
