XM's signal is indeed transparent to many things.

Fiberglass, wood, glass, insulation, etc....

XM recommends putting the antenna on the roof for one reason. The metal you set the antenna on acts as a "dish" of sorts. It helps to reflect the satellite signal towards the antenna element. The home antenna (the antenna supplied with the XMPCR) doesn't have this problem because its actually a antenna element sitting in the middle of a large metal plate. But of course the home antenna is somewhat directional and not suited for use in a car.

Now if you live in a area where some repeaters are located then you should have no problem putting the antenna on your dash. However without repeaters you are likely to have dropouts as long as the antenna is inside the car.


Vladig: The Chicago area has about 20+ repeaters of varying broadcast strength. More then likely your receiver is using a repeater signal most of the time.