| 摘要 |
PURPOSE:To make a center frequency of an intermediate frequency signal coincident with a demodulation center frequency, by shifting the demodulation center frequency to the center frequency of a shifted intermediate frequency signal if the center frequency of the intermediate frequency signal is shifted from the demodulated center frequency. CONSTITUTION:If the center frequency of the intermediate frequency signal is shifted from the demodulated center frequency, a potential difference produced between the frequencies is detected at a potential detection circuit 6, a correction voltage in response to the potential difference is applied to a varactor diode 5 via a sampling circuit 8 from a voltage amplifier 7, the tuning frequency of a tuning circuit 4 is changed, the demodulated center frequency is shifted to the center frequency of the intermediate frequency signal, and when the circuit 6 detects the zeroed potential difference, the operation of the center frequency correction loop is stopped. Thus, the trouble of the adjustment of the demodulation circuit and the tuning circuit is omitted at the manufacture of products, allowing to reduce the manufacture cost. |
