Sirius Satellite Radio

Sirius originally used three SS/L-1300 satellites, instead of GEO satellites, to form an inclined elliptical satellite constellation. Sirius says the elliptical path of its satellite constellation ensures that each satellite spends about 16 hours a day over the continental United States, with at least one satellite over the country at all times. Sirius completed its three-satellite constellation on Nov. 30, 2000. A fourth satellite will remain on the ground, ready to be launched if any of the three active satellites encounters transmission problems. ­In 2006, Sirius purchased a GEO satellite because of its superior signal delivery. The GEO satellite will supplement the elliptical satellites, not replace them. It is currently under construction, and a launch is planned for fall 2008.

The Sirius system is similar to that of XM. Programs are beamed to one of the three Sirius satellites -- the satellites then transmit the signal to the ground, where your radio receiver picks up one of the channels within the signal. Signals are also be beamed to ground repeaters for listeners in urban areas where the satellite signal can be interrupted.

Just like XM Radio, Sirius currently offers a monthly subscription for $12.95 per month. Sirius produces car radios and home entertainment systems, as well as car and home kits for portable use. The Sirius receiver includes two parts: the antenna module and the receiver module. The antenna module picks up signals from the ground repeaters or the satellite, amplifies the signal and filters out any interference. The signal is then passed on to the receiver module. Inside the receiver module is a chipset consisting of eight chips. The chipset converts the signals from 2.3 gigahertz (GHz) to a lower intermediate frequency. Sirius also offers an adapter that allows conventional car radios to receive satellite signals.

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