An essential device on a satellite that plays a crucial role in communication. It serves as a receiver and transmitter, enabling the satellite to receive signals from a ground station, amplify and modify them, and then retransmit them back to Earth.

The primary function of a transponder is to facilitate two-way communication between the satellite and Earth. When a ground station sends signals to the satellite, the transponder receives those signals and processes them. It amplifies the weak incoming signals to a stronger level for better transmission quality and performs necessary modifications or conversions, such as frequency shifting or modulation/demodulation.

After processing and modifying the signals, the transponder then retransmits them back to Earth. The amplified and modified signals are broadcasted over a specific frequency band or channel, allowing ground-based receivers to pick up the signals and extract the transmitted information.