A METHOD AND APPARATUS FOR RECEIVING AN AMPLITUDE MODULATED RADIOSIGNAL

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 analysing circuit (8) under the control of the microprocessor (6) for suppressing noise in the received signal.