Technical
Transponder
A satellite payload component that receives an uplink signal, shifts its frequency, amplifies it, and retransmits it on the downlink.
A transponder is the basic channel unit of a communications satellite. It receives signals from the ground on an uplink frequency, translates them to a downlink frequency, amplifies them, and retransmits them to coverage areas.
Transponder capacity (number and bandwidth of channels) defines a satellite's commercial throughput, and the frequencies used are governed by ITU coordination and national spectrum licences.