Hummer 2008 H2 - Manual (Page 268)

XM™ Satellite Radio Service
XM™ Satellite Radio Service gives digital radio
reception from coast-to-coast in the 48 contiguous
United States, and in Canada. Just as with FM, tall
buildings or hills can interfere with satellite radio signals,
causing the sound to fade in and out. In addition,
traveling or standing under heavy foliage, bridges,
garages, or through tunnels could cause loss of the XM
signal for a period of time. The radio may display NO XM
SIGNAL to indicate interference.
Fixed Mast Antenna
The fixed mast antenna can withstand most car washes
without being damaged. If the mast should ever become
slightly bent, straighten it out by hand. If the mast is badly
bent, replace it.
Check occasionally to make sure the mast is still
tightened.
XM™ Satellite Radio Antenna
System
The XM™ Satellite Radio antenna is located on the roof
of your vehicle. Keep this antenna clear of snow and
ice build up for clear radio reception.
If your vehicle has a sunroof, the performance of the
XM™ system may be affected if the sunroof is open.
Loading items onto the roof of your vehicle can interfere
with the performance of the XM™ system. Make sure
the XM™ Satellite Radio antenna is not obstructed.
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