I went through two phases with this. The first phase I used the FM modulation built into the XM receiver and just put the magnetic antenna on the roof (centered and small in the picture below):

[img]http://4x4icon.com/crossfire/pioneer_tuner/DSC07535.jpg[/img]
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In the second phase I left the antenna where it is but replaced the head unit so I could plug the XM receiver directly into the stereo, eliminating the FM modulation. This greatly improved the sound quality and also gave me addition benefits from the head unit that the factory one didn't offer:


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