transponder
tranz-PON-der
/trænˈspɒndər/
An airborne radio transmitter-receiver that automatically emits an identifying signal in response to radar interrogation.
Transponders transmit unique four-digit four-octet squawk codes along with altitude data to air traffic controllers.
The story behind the word. Coined during World War II from 'transmitter-responder'. Developed for IFF (Identification Friend or Foe) systems to prevent friendly air forces from shooting down their own aircraft.
Word relationships
- beacon: A beacon broadcasts continuously in all directions, while a transponder replies when queried by radar.
Commonly confused with
- transmitter: A transmitter only sends signals out; a transponder (TRANSmitter + resPONDER) responds to incoming signals.
Word family
- transpond (verb): To send a response signal automatically.
Collocations
- transponder code
- squawk transponder
- transponder failure
- mode C transponder
Example sentences
- "Squawk code four-seven-two-one on your transponder for radar identification." Air traffic identification
- "The pilot set the transponder to squawk seven-seven-zero-zero to signal a emergency." Emergency protocol
Memory hook
It TRANSfers a resPONDing signal to radar. Automatic radar identity device.
When not to use
Do not confuse with a basic radio transmitter; a transponder specifically responds to interrogation signals.
Fun facts
- Code 7500 on a transponder secretly alerts air traffic control that an aircraft has been hijacked.
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