Circuitry and method for receiving and decoding a data stream without a preamble transmitted from the transmitting device. The invention includes circuitry in the receiver or interrogation unit for generating a simulated preamble signal that is provided to the input of an averaging circuit and a comparator. The averaging circuitry then averages the simulated preamble signal and the actual received data signal to avoid loss of messages and information data at the front end of the received signal from a transponder.