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The green IDENT button is marked "ID". A transponder (short for transmitter-responder [1] and sometimes abbreviated to XPDR, [2] XPNDR, [3] TPDR [4] or TP [5]) is an electronic device that produces a response when it receives a radio-frequency interrogation. Aircraft have transponders to assist in identifying them on air traffic control radar.
Many modern automobiles have keys with transponders hidden inside the plastic head of the key. The user of the car may not even be aware that the transponder is there, because there are no buttons to press. When a key is inserted into the ignition lock cylinder and turned, the car's computer sends a signal to the transponder.
When the transponder receives an interrogation request, it broadcasts the configured transponder code (or "squawk code"). This is referred to as "Mode 3A" or more commonly, Mode A. A separate type of response called "Ident" can be initiated from the airplane by pressing a button on the transponder control panel.
The following list shows specific aeronautical transponder codes, and ranges of codes, that have been used for specific purposes in various countries. Traditionally, each country has allocated transponder codes by their own scheme with little commonality across borders. The list is retained for historic interest.
There are two key differences, however. One is that the interrogation pulse is followed by a 12-bit code similar to the ones sent back by the Mark 3 transponders. The encoded number changes day-to-day. When the number is received and decoded in the aircraft transponder, a further cryptographic encoding is applied.
An implantable RFID tag or transponder can also be used for animal identification. The transponders are better known as PIT (Passive Integrated Transponder) tags, passive RFID, or "chips" on animals. [70] The Canadian Cattle Identification Agency began using RFID tags as a replacement for barcode tags.
IFF Mark X was the NATO standard military identification friend or foe transponder system from the early 1950s until it was slowly replaced by the IFF Mark XII in the 1970s. It was also adopted by ICAO, with some modifications, as the civilian air traffic control (ATC) secondary radar (SSR) transponder.
Transponders typically have 4 operating modes: Off, Standby, On (Mode-A), and Alt (Mode-C). On and Alt mode differ only in that the On mode inhibits transmitting any altitude information. Standby mode allows the unit to remain powered and warmed up but inhibits any replies, since the radar is used for searching the aircraft and exact location ...