Importance

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Abstract

An AM/FM modulation scheme is presented for optimizing communications between a remote control device held by a user and a receiving unit installed in a vehicle. Historically, these systems communicated with amplitude modulated signals having good range but poor immunity to ambient random radio frequency noise. Frequency modulated systems provide improved immunity to noise however at the expense of range. The object of this invention is to use two or more modulation modes to combine their advantages. A scheme has been devised whereby circuitry capable of alternately operating in at least two modes is used. The same information is therefore transmitted using two or more modulation techniques in succession. The receiving unit also has circuitry and has listening cycles ensuring eventual synchronization with the transmitting unit. If one mode fails due to distance or ambient noise, the other can then attempt to establish a link.

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First Claim