| 摘要 |
PURPOSE:To prevent the genuine signal from being unclear spurious image interference, by sampling the local oscillation frequency with a value corresponding to the frequency between stations. CONSTITUTION:If the signal fed from a local oscillation circuit 1 to a sampling circuit 7 is 100.,120MHz, since the sampling frequency is set to 100kHz, the beat output of 20kHz is produced, this beat output is ''H'' level signal via a high-pass filter 8, it is fed to the gate of FETQ3, which is turned on, to decrease the gain of a DC amplifier 18, allowing to make inoperative the control to a varactor diode D1. If the signal from the local oscillation circuit 1 is about an integral multiple of 100kHz, FETQ3 is off, the gain of the DC amplifier 18 is increased and the local oscillation frequency can be controlled. |
