| 摘要 |
PURPOSE:To test characteristics of tuning, etc., precisely by controlling a local oscillation frequency so as to make a detection output maximum. CONSTITUTION:An AM-modulated carrier signal of 1MHz is applied from an oscillator 9 to the input terminal of an IC1 for AM radio. The detection output signal of the IC1 is amplified by an amplifier 21 and then converted into a DC signal by a DC amplifier 22. A comparator 23 compares the output of the DC amplifier 22 with the output of the amplifier 22 passed through a resistance R1 and a capacitor C1 to output a detection sinal when the detection output is maximum. A gate circuit 25 is opened by a start signal from a starting circuit 26 and closed by the detection signal from the comparator 22. A DC voltage supplied through the gate circuit 25 is integrated by a resistance R2 and a capacitor C2 and then held, thus controlling the oscillation frequency of a local oscillator 4. |
