I read Intersil's response to FCC 01-278. It was pretty amusing. See my news article.

The Sirius system uses three satellites in conjuction with repeaters located in larger metropolitan areas arranged in a cellular grid, re-using their satellite frequencies. It appears that their link budget has only 6.8dB of link margin built into it. Also, their antennas are spray-painted patch antennas on the rooves of cars.

From what I have seen, their repeaters are trying to fill-in to urban canyons and other dead spots. They are being forced by city governments to use the same sites that cellular providers are using - 8 mile diameter cells. This means that they are going up to four miles with about 10-50 Watts ERP. Any minor source of interference causing any little noise over the dead silence of the Big Bang interferes with these folks.

If the XM repeater and the Sirius repeater are not co-located, the two services will probably desense the mobile's receiver on the adjacent band. This is the same hard lesson that Qualcomm had to learn about CDMA - as the noise floor increases, the cell sizes decrease. And since they don't have variable data rate, there is no signal to recover. The outside of the pie is the largest area of course, so you guessed it. They service has huge dead zones on the fringes of their coverage.

I think they may have problems due to poor RF systems engineering. They are discovering that their systems are marginally engineered and grasping at straws. I don't think they will get the FCC's support to cover up for their mistakes.

Konrad Roeder kroeder@springswireless.com