Astra Digital Radio
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Astra Digital Radio (ADR) is a system used by SES Astra for digital radio transmissions on their Astra 1 satellites, using the audio subcarrier frequencies of analogue television channels. It was introduced in 1995. As of February 2008, there are still 51 stations transmitting in this format.
The format uses one mono audio subcarrier, which would normally be allocated to an additional sound track or radio station, or half of a stereo sound track/station. The carrier is digitally modulated, and carries a 192 kbit/s, 48 kHz sampled MPEG-1 Layer II (MP2) encoded signal. 9.6 kbit/s is available for data.
Special receivers are required to listen to ADR stations, although some combined analogue/digital satellite boxes as well as later normal analogue boxes are equipped to decode it.
ADR is incompatible with DVB-S, although DVB-S digital radio stations are also transmitted using MP2 and generally at the same bitrates. As a result, when the final analogue switch-off on the Astra 1 satellites occurs, ADR will become obsolete. However, SES Astra state that 12.2 million homes, almost entirely in Germany, still use their analogue services [1] and does not expect an analogue switchoff to happen until 2010 [2]
The majority of channels to have ever broadcast on ADR, and all remaining ones, are German or in the German language. In some ways, the system is seen to have replaced the "Digitales Satellitenradio" system, dating from the 1980s, which used an entire satellite transponder to carry 16 PCM encoded radio stations, and which closed in 1999.
