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A transponder is an electronic device that wirelessly receives and transmits signals. It was originally used for aircraft identification during World War II and is still used in aviation today. It is also used for electronic toll systems, emergency location services, and television broadcasting.
A transponder is an electronic device used to receive and transmit electrical signals wirelessly. Fittingly, its name derives equally from the words “transmitter” and “responder”. It was originally developed to be attached to an object that needed to be located, and some are still used this way today.
This device works by receiving a signal, called an “interrogator” because it actually “asks” for information, then automatically broadcasts a radio wave at a predetermined frequency. To transmit a signal on a different frequency than the received one, a frequency converter is integrated. By receiving and transmitting on different frequencies, the two signals can be detected simultaneously.
The first use of a transponder was on an aircraft during World War II, as part of the identification friend or foe (IFF) system. By responding to covert interrogation frequencies, pilots could indicate to radar operators that they were friendly aircraft.
These devices are still common today in both military and commercial aviation. They receive a signal from the ground, then automatically respond with an identification code for air traffic controllers, as well as altitude information. In aviation applications, they are also configured to amplify the signal in order to make aircraft more visible on radar.
They are also used to measure distance by calculating the time elapsed between sending the interrogator signal and receiving the transponder signal. For example, sonar devices are used to mark underwater locations, calculate depth, and track locations.
It may seem like this is a technology the average consumer never uses, but while that used to be the case, it’s not anymore. The modern commuter probably has at least one transmitter in his car, probably mounted on the windshield or dashboard. These are for roads that use electronic toll systems that calculate the amount of tolls payable and complete the transaction without requiring the driver to roll down the window. Some newer cars are also equipped with ones that operators can use to locate the vehicle in an emergency. Cell phones use a similar, albeit smaller, chip to send the phone’s location when used to call an emergency number.
Even the occasional television viewing often involves the use of these devices. A network can connect its terrestrial satellites to Earth-orbiting communications satellites, send multiple channels of digitally compressed video and audio to a single onboard transponder, and local stations can then pick up the program and rebroadcast it locally aiming the dish at base of land appropriate.
