One of two possible modes of operation for a PIT–tag interrogation system. In FDX systems, the tag is continuously energized while in the antenna field; it then continuously modulates the electromagnetic field, producing a unique pattern, which is processed by the transceiver to yield a unique tag code.
We refer mainly to FDX systems, specifically the FDX–B 134.2–kHz system, whose technologies are based on ISO standards 11784 and 11785. For an overview of how FDX PIT–tag systems function, see Beigel (1999).
The passive integrated transponder (PIT) is a type of radio frequency identification (RFID) used extensively in fisheries research. The PIT tag is relatively inexpensive (~$3 per tag) and can yield high returns of information, with detection rates in the high 90% range for fish that come within reading range of a detection system.
Encased in glass, the standard 12.5–mm PIT tag is biologically inert and can be injected with a hypodermic needle into salmonids as small as 60 mm.