Track to train communications systems

Abstract From the Canadian patent

Track to Train Communications Systems A transponder circuit comprises a loop (4) for inductively coupling with an interrogator (2) to transmit a binary coded message to the interrogator (2). The loop (4) forms part of a tuned circuit which is tuned to a first resonant, frequency Fc and which is detunable by an associated modulator to a second, lower frequency Fc/2 whereby a binary code can be created utilising said two frequencies. Advantageously a binary '1' and a binary '0' each comprise two cycles of Fc and one cycle of Fc/2 with a binary '0' having the reverse sequence of the frequencies to a binary ' 1 ' .