Honda Civic Owner's Manual page 164

Audio System (Models with navigation system)
Signal may be blocked by
mountains or large obstacles
to the south.
SATELLITE
158
Signal weaker in
these areas.
GROUND REPEATER
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. Carrying
large items on a roof rack can also
block the signal.
Depending on where you drive, you
may experience reception problems.
Interference can be caused by any of
these conditions:
Driving on the north side of an
east/west mountain road.
Driving on the north side of a
large commercial truck on an
east/west road.