What is a Transponder?

About Transponder:

• A transponder is a wireless communication, monitoring, or control device that picks up and automatically responds to an incoming signal. 
• The term is a combination of transmitter and responder.
• Transponders are typically used for detecting, identifying, and locating objects, but they can also be used in other technologies, such as satellites to relay communications signals.
• Transponders are commonly found in both civilian and military aircraft and in objects, such as car keys.
• How do transponders work?

• Transponders operate using radio frequencies and respond to wireless monitoring, communications, and control device signals.
• When sent a signal-also called an interrogator-a transponder responds by returning an identifying signal. 
• The information included in the response varies depending on the type of transponder but can include location and identifying codes.
• The transponder automatically sends back a radio signal at a predetermined frequency. 
• To receive and send signals simultaneously, receiving and transmitting signals must be set at different frequencies.
• For Example: An air traffic controller can send an interrogator signal and receive identifying information on an aircraft. This enables the control tower to track the aircraft in the surrounding airspace and provide other information to help the pilots maintain adequate distance from other aircraft.

• Transponders are used with the following technologies:

• aircraft identification;
• communications satellites;
• vehicle keys;
• optical communications;
• sonar;
• electronic toll collection systems;
• lap timing and tyre identification for motorsports; and
• magnetic labels on credit cards.