Patent ID: 8559486

Claim:
An RF tag system for conducting radio communications between an RF tag reader and an RF tag using radio waves of VHF band or above (30 MHz or above), comprising: the RF tag configured as at least one of a remote start RF tag and a scheduled start RF tag, and the RF tag reader, the RF tag reader being constructed and arranged to send a tag activating command including RF tag ID code of an RF tag on the other end of communications in ASK modulation mode by using a CW radio wave at a query carrier frequency fo, and receiving a response signal as a return information, which is superimposed on a sub-carrier signal frequency-offset by a frequency fs from the query carrier frequency fo, from the RF tag, wherein the remote start RF tag includes a resonant stub voltage multiplier circuit that detects a query from the RF tag reader and a pulse code key detecting circuit that determines whether a pulse width is within a certain range, wherein the scheduled start RF tag includes a resonant stub voltage multiplier circuit that detects a query from the RF tag reader and a demodulation circuit that is driven by a timer at regular time intervals, and wherein the RF tag reader includes a quadrature and compensation circuit that directly conducts quadrature detection by the query carrier frequency fo and then corrects detection error, and a generating circuit that samples signals at a frequency 4 fs in order to obtain an MPSK demodulated signal from a detection signal.