Editing Transponder (section)

==Aviation==
<!-- This section is linked from [[SR-71 Blackbird]]. -->
{{Details|Transponder (aeronautics)}}
[[File:Transponder in Private Aircraft.jpg|thumb|A transponder in a private plane squawking 2000]]

Another type of transponder occurs in [[identification friend or foe]] (IFF) systems in [[military aviation]] and in [[air traffic control]] [[secondary surveillance radar]] (beacon radar) systems for [[general aviation]] and [[commercial aviation]].<ref>{{cite journal |last1=Dobkin |first1=Daniel M. |title=A Radio-Oriented Introduction to Radio Frequency Identification |journal=High Frequency Electronics |date=2005}}</ref> 

[[Radar|Primary radar]] works best with large all-metal aircraft, but not so well on small, composite aircraft. Its range is also limited by terrain and rain or snow and also detects unwanted objects such as automobiles, hills and trees. Furthermore, it cannot always estimate the altitude of an aircraft. [[Secondary radar]] overcomes these limitations but it depends on a transponder in the aircraft to respond to interrogations from the ground station to make the plane more visible.{{cn|date=May 2024}}

Depending on the type of interrogation, the transponder sends back a [[transponder code]] (or "squawk code", Mode A) or altitude information (Mode C) to help air traffic controllers to identify the aircraft and to maintain separation between planes. Another mode called Mode S (Mode Select) is designed to help avoiding over-interrogation of the transponder (having many radars in busy areas) and to allow automatic collision avoidance. Mode S transponders are [[backward compatible]] with Modes A and C. Mode S is mandatory in [[controlled airspace]] in many countries. Some countries have also required, or are moving toward requiring, that all aircraft be equipped with Mode S, even in [[uncontrolled airspace]]. However, in the field of general aviation there have been objections to these moves, because of the cost, size, limited benefit to the users in uncontrolled airspace, and, in the case of [[balloon (aeronautics)|balloons]] and [[Glider (sailplane)|gliders]], the power requirements during long flights.{{cn|date=May 2024}}

Transponders are used on some military aircraft to ensure ground personnel can verify the functionality of a missile’s [[flight termination system]] prior to launch. Such radar-enhancing transponders are needed as the enclosed weapon bays on [[Fifth-generation jet fighter|modern aircraft]] interfere with prelaunch, flight termination system verification performed by [[range safety]] personnel during training test launches. The transponders re-radiate the signals allowing for much longer communication distances.<ref>{{Cite web|url=https://www.curtisswrightds.com/infocenter/white-papers/telemetry-re-radiation-system.html|title=TELEMETRY RE-RADIATION SYSTEM|last=Cook|first=Paul|date=2008|website=Curtiss-Wright Desfense Solutions}}</ref>

===Marine===
The [[International Maritime Organization]]'s [[International Convention for the Safety of Life at Sea]] (SOLAS) requires the [[Automatic Identification System]] (AIS) to be fitted aboard international voyaging ships with {{GT|300 or more|disp=long}}, and all passenger ships regardless of size.<ref>{{cite web
 |work        = [[International Convention for the Safety of Life at Sea|SOLAS]]'1974
 |url         = http://www.imo.org/KnowledgeCentre/ReferencesAndArchives/HistoryofSOLAS/Documents/SOLAS%201974%20-%20Brief%20History%20-%20List%20of%20amendments%20to%20date%20and%20how%20to%20find%20them.html#43
 |title       = December 2000 amendments
 |author      = International Maritime Organization
 |url-status     = dead
 |archive-url  = http://arquivo.pt/wayback/20140725015425/http://www.imo.org/KnowledgeCentre/ReferencesAndArchives/HistoryofSOLAS/Documents/SOLAS%201974%20-%20Brief%20History%20-%20List%20of%20amendments%20to%20date%20and%20how%20to%20find%20them.html#43
 |archive-date = 2014-07-25
}}</ref> AIS transmitters/receivers are generally called ''transponders'', but they generally transmit autonomously, although [[Coast radio station|coast stations]] can interrogate [[Automatic identification system#Detailed description: Class B units|class B transponders]] on smaller vessels for additional information.{{cn|date=May 2024}} In addition, [[navigational aid]]s often have transponders called [[Racon|RACON]] (radar beacons) designed to make them stand out on a ship's radar screen.{{cn|date=May 2024}}

[[Sonar]] transponders operate under water and are used to measure distance and form the basis of underwater location marking, position tracking and [[navigation]].