Imagine being able to listen to CD-quality music while driving down a shady boulevard or cruising a crowded highway. That’s the promise of satellite radio, which offers uninterrupted, commercial-free music beaming down from space to your car’s FM radio with crystal clear quality. But how does it work?
In 1992, the Federal Communications Commission allocated a section of the 2.3 GHz spectrum for digital satellite radio broadcasting. Two companies, XM and Sirius, paid more than $80 million each to use that frequency band, which can reach anywhere in the United States. They launched satellites, which orbit the planet in geostationary orbit about 22,000 miles from Earth, and terrestrial “repeaters” stationed throughout the country to help get the signal past tall buildings and other obstacles.
The satellite signals are received by a receiver in your car, home stereo or portable boombox, which has a specialized antenna to pick up the signal. The radio’s baseband processor digitizes, demodulates, error-corrects and deinterleaves the satellite data streams. It then stores four seconds of each of the three satellite and terrestrial signal arrivals in a memory device called a Maximum-Ratio Combiner, which brings them into time coincidence and combines them for playback.
The resulting digital audio is played over an analog-to-digital converter, which converts the digital stream into a stream of radio waves that travels to your car’s FM tuner. The radio’s receiver sends the signals to your car’s stereo, where they are interpreted as a stream of 175 channels of commercial-free music and entertainment, including talk radio and news channels.
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