A transponder for use in an object indentification system including an interrogator which transmits a continuous interrogation signal and detects a responsive identification signal transmitted by the transponder. The transponder receives and detects the interrogation signal and, in response to receipt of the interrogation signal, produces a repeating identification signal having a fixed number of binary bits consisting of an identification data portion of a specified number of consecutive bits less than one half of the fixed number of bits, and a synchronization pattern of consecutive bits consisting of first, second and third bits of alternating binary values, a consecutive sequence of a plurality of bits which are all of the same binary value as the second bit, and a single bit of the same binary value as the first and third bits. The identification signal is modulated onto a carrier signal and transmitted. Preferably, the first, second and third bits and the sequence of a plurality of bits constitute one half of the fixed number of binary bits of the identification signal, with the binary value of the first bit being a binary 1.
IMPROVED TRANSPONDER FOR PROXIMITY IDENTIFICATION SYSTEM