I had the dealer install Sirius in my TCH and the antenna is attached to the windsheild behind the passenger side of the rear view mirror. I haven't noticed any signal loss from this configuration. I've had 100% coverage except under overpasses and very heavy tree lined streets in CT(virtually no line of sight). I had an after market Sirius system installed in my other car about 3 years ago with the attenna mounted on the outside. I haven't noticed any difference in reception between the 2 installations.