| 摘要 |
PURPOSE:To stabilize broad band tuning byf making it possible to select the oscillation frequency band of a variable oscillator independently of an intermediate frequency by obtaining a local oscillation frequency signal from the difference in frequency between the variable oscillator and a fixed oscillator. CONSTITUTION:Of the television tuner, local oscillating circuit 6 consists of variable oscillator 61, fixed oscillator 62 and mixer 63 and the frequency difference between oscillators 61 and 62 is generated as a local oscillation frequency signal. For this purpose, a relatively high frequency band of 3,150-3,824MHz, etc., is used for oscillator 61 and the local oscillation frequency of oscillator 62 is only set to 3,000MHz so as to set the local oscillation frequency in the normally used range of 150-824MHz for the single conversion system. Consequently, an input signal to mixer 5 is converted into a signal of the current intermediate frequency, which is outputted to tuner output 7. Thus, the oscillation frequency of variable oscillator 61 can be selected in the variable range of the variable tuning element independently of the intermediate frequency. |
