| 摘要 |
PURPOSE:To use a filter easy for its manufacture and to improve the noise characteristics, by passing through a signal to a narrow-band filtering means to suppress unnecessary oscillatin mode after converting the signal into a low frequency. CONSTITUTION:Denoting a main oscillation frequency passig through a series circuit consisting of a surface acoustic wave filter delay element 1 and an amplifier 4 as fA and an oscillation frequency of a local oscillator 7 as fB, when a difference frequency (fA-fB) is generated at the 1st frequency mixer 8, a band- pass filter 6 can use a comparatively low frequency, then a filter with stable characteristics such as quartz filter can be used. The 2nd frequency mixer 9 is mixed with (fA-fB) and fB to generate the fA again. |
