Abstract: An improved communication apparatus for communicating between a first object and a second object wherein the first object includes apparatus for generating and transmitting a transmit signal and the second object includes apparatus for receiving the transmit signal and providing an emitted signal in response thereto, the emitted signal having a frequency coherently related to the frequency of the received transmit signal. The second object also includes an apparatus for encoding an identifying code having a unique code format wherein the beginning and the end of the code format are identifiable, the first object including apparatus for receiving the encoded emitted signal, identifying the code format encoded therein and determining the received emitted signal represents a valid code format.