| 摘要 |
PURPOSE:To carry out the IF offset adjustment or the like in an easy and accurate way, by inserting the frequency converting circuit into the signal route between the variable frequency oscillator and the phase comparator and then varying the frequency of the output signal of the frequency converting circuit. CONSTITUTION:Frequency converting circuit 21 comprising mixer 17, oscillator 18 and BPF19 is inserted into the signal route between variable frequency oscillator VCO forming local oscillator 14 and phase comparator 25, and thus the frequency conversion is given to the output of oscillator 14. When the channel is selected, control voltage VCX of oscillator 18 is varied previously and frequency fX of the output signal is controlled to fX=fi (fi: central frequency of intermediate frequency filter). This means that the IF offset adjustment is carried out. In other words, in case frequency fi is shifted as fi1, fi2...fin in the tuner and every unit, frequency fX is made to correspond to fin to secure fX=fin. As a result, the tuning point set with preset value N can be turned into the perfect tuning point at all times. Thus the tuner can carry out an easy offset adjustment. |
