Low power density radio systems

A low power density radio system is provided using a simple FSK transmitter arranged to transmit very short bursts to a receiver at predetermined frequent intervals. Such a system can be used between a meter transponder and a reader in an AMR system to eliminate the need for a receiver in the transponder and still achieve extended battery life. The problems of detecting and demodulating the short burst are overcome by using a sample and hold circuit that detects a preamble signal of reversals to indicate the presence of the burst. The sample and hold circuit also provides the reference value to correct for the DC pedestal voltage that arises as a function of the transmitter and receiver frequency errors. The data signal that follows the preamble signal can then be detected, and is followed by a verifying signal as part of the signal burst. The burst signal is repeated at predetermined intervals and is preferably only {fraction (1/4000)} or less than the signal time interval.