For surviving those long hours in the pickup and tractor cab, a radio provides entertainment, news and makeshift companionship. But like an eccentric friend who overstays his welcome, commercial radio can get on your nerves, too.

Soon, a network of geostationary satellites and ground-based repeating stations could change the way you listen to music, news, talk and weather on the radio. Two companies, Sirius Satellite Radio and XM Satellite Radio, are set up to bring crystal-clear digital radio signals and extensive program variety to anyone with a satellite radio. It may be the biggest change on the airwaves since the introductio of FM 40 years ago.

In the southwestern United States, XM Satellite Radio is already delivering 100 channels of music and talk for $9.99 a month. A full nationwide launch is set for mid-November. For the listener, the downside of XM is that many of its stations will be subsidized by commercials.

Sirius Satellite Radio will broadcast all of its music commercial-free, but charge a monthly fee of $12.95/month, when it rolls out its service nationwide sometime in December.

How it works. Satellites hovering in geostationary orbits above the United States send a radio signal down to Earth. To pick it up, you need a small antenna mounted on the roof of your house or vehicle. Because the signal comes from above, much like a global positioning system signal, it can be blocked by tall buildings, canyon walls or heavy leaf cover. That’s not generally a problem in farm country though.

For complete coverage in city and country, XM uses two satellites and 1,000 ground-based repeaters, or mini radio towers, in 70 major metropolitan areas. Sirius uses three satellites and fewer repeaters. Both companies’ systems are expected to offer complete coverage across the country, letting you drive coast to coast with no interruption in the audio signal. The digital signal eliminates static, fuzz and background noise on music channels ranging from bluegrass, heavy metal, country and western, oldies, rap, classical, blues, reggae and opera. News/talk programming includes the BBC, Bloomberg, C/Net, CNN, Discovery Channel, ESPN, The Weather Channel and several comedy channels.

Installation. In 2002, many automobile and truck manufacturers will begin offering satellite radio as a factory-installed option. If you don’t want to buy a new vehicle just to get satellite radio, getting it installed is similar to putting in a conventional car stereo. The main difference is that a small antenna mounted on the roof or rear window, either magnetically or with adhesive. A wire runs from the antenna to a small receiver that can be hidden under a seat or in the trunk. Another wire runs from the receiver to the car radio. The cost of all the hardware and installation starts at about $400.

A less expensive approach is the “plug-and-play” XM01 satellite receiver from Sony for $299. It plugs into the cigarette lighter for power and has a cassette adapter similar to those that portable CD players use to get sound to a car’s audio speakers.

Sony also sells an AC adapter so the XMO1 can be used inside a house, plugged into a wall outlet and a stereo system. Subscribers in rural regions might have to mount an antenna on the outside of their homes.

For more information, contact Sirius Satellite Radio Inc., 1221 Avenue of the Americas, New York, NY 10020, 212/584-5100, www.siriusradio.com; or XM Radio, 1500 Eckington Place N.E., Washington, DC 20002, 202/380-4000, www.xmradio.com.