2011 Acura MDX Owner's Manual - Page 232

Playing the XM® Radio (Models with navigation system) Signal weaker in these areas. Signal may be blocked by mountains or large obstacles to the south. The XM satellites are in orbit over the equator; therefore, objects south of the vehicle may cause satellite reception interruptions. To help compensate for this, ground-based repeaters are placed in major metropolitan areas. Satellite signals are more likely to be blocked by tall buildings and mountains the farther north you travel from the equator. SATELLITE GROUND REPEATER 228 2011 MDX