Importance

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Abstract

A unique wireless transmission signal structure has a preamble at a first data rate and a data portion including the base band signal at a second, higher data rate. The signal is generated in a manner which ensures that the transmitted signal is 'on' no more than one half the entire transmission time. A unique wireless transmitter generates the inventive transmission signal. A crystal oscillator drives both a signal generation circuit and a frequency generator. This provides accurate timing and allows the transmission signal to be not self-clocked. A unique wireless transmission receiver has adjustable pre-detection and post-detection filters. When the receiver is scanning for an incoming transmission signal, the pre-detection filter has a wide bandwidth to receive incoming transmission signals within a predictable range of variations due to inaccuracies in the transmitter and receiver. At this time, the post-detection filter has a narrow bandwidth to pass the low bit rate preamble data and reject noise. When a preamble has been detected, the incoming signal is 'locked onto' and the pre-detection filter is adjusted to a narrow bandwidth which reject signals other than the incoming signal. The post-detection filter is switched to a wide bandwidth to accept the higher data rate data/CRC portion of the signal. This arrangement allows the transmitter to be relatively inexpensive and to transmit efficiently maintaining short on air time yet the receiver may be selected and sensitive.

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First Claim