Digital television allows us to be more efficient and enables us to bundle a number of television services together into what is known as a multiplex. Each multiplex can then be broadcast from a satellite using an individual frequency. Your television or set top box can then pull out each individual service from the multiplex and allow you to access it. This allows a number of multiplexes to be transmitted from each satellite and a wider range of services to be broadcast.
Using a multiplex enables us to broadcast a number of television channels at once using just a single frequency. This allows broadcasters to use the spectrum allocated to satellite services to the maximum extent, giving you more television services to choose from. We can also add in radio services, Red Button data services, subtitles and audio description into a multiplex. Each multiplex also carries the service information which includes the data needed for EPG’s.
The term transponder is often interchanged with multiplex. This is technically incorrect as a transponder is just a set of equipment that operates at a particular frequency and both receives and re-transmits the multiplexed services.
What channels are available on which multiplexes?
The easiest way to find out is to look for transponder lists, as most multiplexes do not have obvious names.