Transmitter-receiver device on a satellite that transmits signals automatically when it receives predetermined signals. The term “satellite transponder” refers collectively to a transmitter-receiver subsystem on board the satellite that processes, amplifies and retransmits a range of frequencies (the transponder bandwidth) to another location/terminal/antenna on the earth. There are many transponders on a typical satellite, each capable of supporting one or more communication channels. In a few limited instances, satellite transponders can transmit directly to other satellites; this is known as satellite mesh topologies. These systems tend to be more expensive to build, and services are more expensive for end users.