| 摘要 |
PROBLEM TO BE SOLVED: To suppress noise by muting a detection signal appropriately even when the strength of electric field of an incoming radio wave falls off rapidly. SOLUTION: A first envelope signal EV is generated from an IF signal SIF and passed through a low-pass filter 22 having a large time constant to generate a first evaluation signal SP. A level adjuster 23 amplifies the first envelope signal EV to generate a second envelope signal EVH which is passed through a low-pass filter 24 having a small time constant to generate a second evaluation signal SPH. A selector 25 compares the first and second evaluation signals SP and SPH, and an evaluation signal having a larger level becomes a select signal CM. An operator 26 compares the level of the select signal CM with a fixed value VB, and the amount of subtrahend of an attenuator 27 is set at 0 if the level of the select signal CM is smaller than the fixed value VB. Otherwise, the amount of subtrahend of the attenuator 27 is adjusted in accordance with the difference between the select signal CM and the fixed value VB. COPYRIGHT: (C)2008,JPO&INPIT
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