| 摘要 |
PURPOSE:To keep a constant input frequency of a narrow-band BPF and thus realize a measurement of the high-band sweep, by varying the oscillation frequency of a voltage control oscillator with variation of the input frequency. CONSTITUTION:The signal 2 that is filtered by the BPF101 of the input signal 1 is amplified by the amplfier 102 to secure a constant level and then supplied to the switch circuit 103. On the other hand, the branch output 7 of the signal path 3 is mixed with the output of the voltage control oscillator 112 by the mixer 108 to be applied to the narrow-band BPF107. The squelch circuit 109 decides the level of the signal 1 and then switches the circuit 103 so that the output of the oscillaor 105 is turned into the output signal 5 in case when the level of the signal 1 is lower than the prescribed value. The oscillation frequency of the oscillator 12 is controlled so that the input frequency of the BPF107 becomes identical to the central frequency of the BPF107. As a result, a measurement is possible for the wind-band sweep. |
