What Is a Transponder in Reference to Satellites?

Communications satellites have many transponders.

The word "transponder" pictures the two principal actions that the device executes: transmitting and responding. It can transmit messages in response to incoming radio signals. Satellites employ this technology.

Transponders in Satellites

The transponder gives communications satellites the ability to communicate. A typical communications satellite has various transponders that operate at different frequencies.

Radio and Television

Each radio and television station communicates through one of the transponders of a communications satellite. The transponder receives a radio or television broadcast from earth, amplifies it and sends it back down to earth at a slightly higher frequency. The higher frequency will not interfere with the incoming broadcast signals.

Tracking Small Satellites

Students of the United States Naval Academy of Annapolis sent up a small experimental satellite equipped with a transponder. The transponder monitored the position of small satellites imperfectly visible to other radar systems. This may become standard monitoring procedure in the future, according to NASA.

Determining Altitude

Sometimes satellites communicate with a transponder on earth. If a transponder is placed on top of a mountain, an overhead satellite can communicate with this transponder to measure the altitude of the mountain, according to the European Space Agency.

References

• TopBits: Transponder
• European Space Agency: Altimeter Bias Determination Using Two Years of Transponder Observations
• NASA: International Space Station
• Intelsat: Satellite Basics
• The Canadian Encyclopedia: Satellite Communications

Resources

• Educause: Integration of Digital Satellite and Terrestrial Networks for Education and Training