What is transponder bandwidth?

A transponder (short for transmitter-responder and sometimes abbreviated to XPDR, XPNDR, TPDR or TP) is an electronic device that produces a response when it receives a radio-frequency interrogation.

Early Bird had just one transponder capable of sending just one TV channel. The Boeing 702 series of satellites, in contrast, can have more than 100 transponders , and with the use of digital compression technology each transponder can have up to 16 channels, providing more than 1,600 TV channels through one satellite.

A satellite contains multiple channels, called transponders, that provide bandwidth and power over designated radio frequencies. The transponder’s bandwidth and power dictate how much information can be transmitted through the transponder and how big the ground equipment must be to receive the signal .

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 .

A transponder will send an identifying coded signal in response to a transmitted interrogation from a ground-based radar station . An air traffic controller can then view the identified blip on a screen and know who it is and provide direction to the flight crews maintaining adequate separation with other blips.

Basically, there are two types of transponders. Those are Bent pipe transponders and Regenerative transponders .

Each of this transponder occupy part of the total satellite bandwidth (BW) i.e. 500 MHz . Figure-1 depicts transponder channels with each utilizing 36 MHz of bandwidth from the total BW of 500 MHz. The guard band of 4 MHz is provided between transponders to avoid interference.