Remotely interrogated transponder

A radio frequency transponder for receiving an externally generated signal at first carrier frequency, said externally generated signal being amplitude modulated in accordance with an interrogation signal, and for transmitting a data signal at a second carrier frequency in response to receipt of said interrogation signal, comprising:

• an oscillator circuit including means for producing radio frequency oscillations at said first carrier frequency, said oscillator circuit including means for receiving said externally generated signal;
• quenching circuit means operably coupled to said oscillator circuit for periodically quenching the amplitude of said oscillations in said oscillator circuit;
• sampling means operably coupled to said oscillator circuit for sampling said oscillations in said oscillator circuit and providing a sampling means output in response to the receipt of said externally generated signal by said oscillator circuit;
• tuning circuit means operably coupled to said oscillator circuit for selectively changing the resonant frequency of said oscillator circuit between said first frequency and said second frequency;
• and
• switching means operably coupled to said sampling means and said tuning ciruit means for selectively activating said tuning circuit in response to receipt of said sampling means output whereby said oscillator circuit resonant frequency is shifted from said first frequency to said second frequency in response to receipt of said externally generated signal by said transponder.