The apparatus embodies an inquiry unit with a radio frequency emitter and an answering unit (transponder) with a frequency divider for the frequency of the emitter of the inquiry unit. The divided frequency is modulated with the data inside the transponder as a carrier frequency in a phase modulator...http://www.google.fr/patents/US5327122?utm_source=gb-gplus-shareBrevet US5327122 - Installation for data transmission with correction of phase error
Installation for data transmission with correction of phase error
