| 摘要 |
Receiving apparatus ( 1 ) for receiving an amplitude modulated signal which may be transmitted on a plurality of frequency channels within a predetermined frequency bandwidth comprises a tuner ( 3 ) for sequentially scanning through the channels under the control of a microprocessor ( 6 ) which determines the presence of a signal on a channel to which the tuner ( 3 ) is tuned. A first validation circuit ( 10 ) determines if the received signal is a valid type signal, and if so the microprocessor ( 6 ) counts the channels from the channel on which the signal is first detected to the channel on which the signal can no longer be detected is reached. The microprocessor ( 6 ) determines the middle one of the channels in which the signal is detected, and the microprocessor ( 6 ) locks the tuner ( 3 ) onto the frequency of the middle channel, and simultaneously operates a gate circuit ( 11 ) for outputting at least one complete signal to security apparatus of a motor vehicle for switching the state of the security apparatus from one of an armed and a disarmed state to the other of the armed and disarmed state. A noise suppressing circuit ( 9 ) is responsive to a noise analyzing circuit ( 8 ) under the control of the microprocessor ( 6 ) for suppressing noise in the received signal.
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