| 摘要 |
PURPOSE:To measure easily and with high accuracy unknown frequency, by inputting an output of a modulator for fetching a difference of frequency to be measured and reference frequency, to a band pass filter, making frequency of a reference oscillator variable in accordance with its output level, and setting said difference in the vicinity of constant frequency. CONSTITUTION:When frequency fr of a reference oscillator 3 is set to 10MHz at first in case when frequency to be measured fx is 12,3MHz and difference frequency fp is 1MHz, modulation frequency fx+ or -fr outputted from a modulator 1 becomes 22.3MHz and 2.3MHz, therefore, a band pass filter 2 obstructs it, and the output level becomes a specified value or below. Therefore, when a controlling circuit 4 increases fr by a prescribed step, for instance, 0.1MHz each, when fr is 11.3MHz, fx+ or -fr becomes 23.6MHz and 1.0MHz, fx-fr coincides with fp, and the output level of the band pass filter 2 becomes the specified value or above, therefore, the controlling circuit 4 stops its operation. |
