Satellite Channel

The term channel is often used interchangeably with the word transponder with the same meaning. However, the word channel refers more accurately to the absolute frequency range over which the transponder operates (e.g. 11 GHz +/- 18 MHz), rather than to the amplification process itself.

The process of dividing the available frequency spectrum into separate parts that are suitable for individual high power amplification is usually referred to as channelization. A channel is normally defined by its center frequency and its usable bandwidth.

A carrier's uplink frequency has to be different from its downlink frequency. Consequently, the satellite must also alter the frequency of each carrier. This process is known as frequency translation.

The satellite design frequently offers the possibility of associating an High Power Amplifier (HPA) with different frequency ranges, or channels, which may or may not have the same usable bandwidth. Practically, this is achieved by selecting different filters at the input and output of the HPA, where each set of input and output filters defines a particular channel (frequency range). The HPA can only amplify over one frequency range at a time. The corresponding channel is referred to as an active or operational channel (transponder). The remaining channels are typically referred to as inactive, spare or backup channels (transponders).