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What's a transponder?

Transponders were originally electronic circuits that were attached to some item whose position or presence was to be determined.

The transponder functioned by replying to an interrogation request received from an interrogator, thereby allowing ranging measurements based on time of flight.

Transponders were initially used in World War 2 on aircraft to identify the aircraft using IFF (Identify Friend or Foe), where friendly aircraft would respond to secret preprogrammed interrogation codes and indicate to the radar operators that they were friendly aircraft. Today, transponders are still used extensively on commercial aircraft to relay to the radar operators the height and identity of the aircraft on their radar displays. Transponder systems have recently started to become major players in the field of electronic identification.

Another major category of transponders is the use of transponders in radio relay systems such as fixed/mobile radio networks and satellite transmissions. The same principle applies in that the data is transmitted on a carrier frequency at one frequency, and rebroadcast on a carrier of another frequency, allowing the strong and weak signals to co-exist.

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Viasat LinkStar ModemLinkStar?: Two Way Satellite Internet Access

The DVB-RCS type services are based on cost-effective LinkStar? terminals from ViaSat. Advantages include the ability to share the satellite bandwidth among terminals - both in the upstream (forward channel) and in the downstream (return channel).