| 摘要 |
<p>PROBLEM TO BE SOLVED: To appropriately narrow the band of an on-vehicle equipment, to lower noise and to improve sensitivity by providing a switch, a modulator, an amplifier, a filter, a frequency detector and a control part, etc. SOLUTION: Intermediate frequency signals generated by the output of a first switch 34 are amplified in an intermediate frequency amplifier 41 and outputted to a narrow-band stop filter 48 and a narrow-band pass filter 49. A second switch 50 is in at an ON-state at the beginning of communication, and switch control signals and frequency control signals are outputted from a control part 44 at the moment of detecting an intermediate frequency which passed through the filters 48 and 49 in a frequency detector 51. Through the switch control signals, the second switch 50 is turned to an OFF-state, and reception signals are passed through the narrow-band pass filter 49. Also, through the frequency control signals, the oscillation frequency of an oscillator 33 is controlled, so as to make the intermediate frequency of this on-vehicle equipment to be within the passing band of the narrow-band pass filter 49. Thus, noise is lowered, and sensitivity is improved.</p> |
