Executives at XM Satellite Radio and Sirius Satellite Radio are upbeat. They can boast about signing up more than 3 million subscribers collectively to date, and if their predictions are on target, the two satellite radio companies together will have more than 4 million subscribers by the start of 2005.

XM Satellite Radio enjoys a clear lead in this sector with well over 2.5 million subscribers as of Sept. 30, while second-place Sirius Satellite Radio serves about 800,000 subscribers.

I reviewed XM Satellite Radio for this paper almost two years ago, and recently I plugged in a new portable Sirius satellite radio from Sanyo known as the CRSR-10. This has been designed for use in both the home and car.

Besides Sanyo, Sirius products are available from manufacturers like Alpine, Audiovox, Blaupunkt, Clarion, Eclipse, Jensen, JVC, Kenwood, Panasonic and U.S. Electronics. You can find them at Advance Auto Parts, Best Buy, Car Toys, Circuit City, Crutchfield, Good Guys, Wal-Mart, RadioShack, Sears, Tweeter and Ultimate Electronics.

The contemporary car is being transformed from the standpoint of factory installed onboard entertainment and navigation systems. On the audio side, General Motors now offers the XM radios as an option in 90 percent of its North American cars, while Honda Motor Co. offers XM in 8 cars. SIRIUS radios can be found in cars made by DaimlerChrysler, Ford, BMW, Dodge, Jeep, Nissan, Infiniti, Mazda, Audi, Lincoln-Mercury, Mercedes-Benz, Porsche and Volkswagen.

Jaguar, Volvo, Land Rover and Aston Martin plan to offer Sirius in the near future. A growing number of boat and RV manufacturers are offering these satellite radios as well. BusinessWeek recently reported that 57 percent of the folks who buy satellite radio-equipped cars sign up for the service. In addition to satellite radio, CD and DVD players, look for live satellite TV in the car as an option in the not too distant future thanks to amazing strides in emerging miniature antenna technology.

Sirius is an excellent service, and with 120 channels to select from, including 65 channels of 100 per cent commercial-free music at $12.95 per month, it is certainly giving XM a healthy dose of competition. The Sanyo CRSR-10 which has a price tag of $149.95 is a stylish Sirius unit that features a large display along with ease of operation. While it is a bit bigger than the Delphi Roady radio which XM Satellite Radio introduced a few months ago, it is a top performer which can be moved from home to car and back again in just a few moments.

While Sirius may be seen as the underdog in the satellite radio sector, it no doubt benefits from the publicity that XM generates. For example, Popular Science magazine just announced that a pair of XM units, the Delphi XM SKYFi2 radio and the instantly updated Navteq Traffic-based XM NavTraffic navigation system, are included on its list of the Best of What’s New Award winners. In a world where a rising tide still lifts all ships, this satellite radio story is very much a work in progress.

In Maine, Sirius seems to provide slightly better coverage than XM. While no scientific survey has been completed, there are preliminary indications that in the areas where XM might be blocked for only a few seconds by a steep hill or mountain situated directly to the southwest, Sirius keeps right on playing.

This phenomenon can be attributed to two things, either that Sirius satellites are higher in the sky over North America than the XM satellites or because of a different software configuration. Regardless, this slight edge in Sirius reception in Maine has been observed in at least 3 zones where I routinely experience a temporary blockage of XM service, if only a matter of seconds, a brief signal dropout in hilly terrain. XM reception statewide overall is impressive.

So, if you are a jazz enthusiast or if other musical genres appeal to you, give both XM and Sirius a good look. Like DirecTV and Echostar in the satellite TV arena, there are subtle differences in the programming, and increasingly, lots of good receivers to choose from. If you want to try something different, especially for those frequent long trips in your car and if MP3s and CDs have lost their edge, give satellite radio a try.

Peter J. Brown, a free-lance writer from Mount Desert, specializes in satellite technology.