You have to understand that in comparison to the repeater signal, the actual satellite signal that reaches you on the ground is VERY weak. Unfortunately the frequesncy of XM's signal is very close to the famous 2.4 Ghz signals used by almot every cordless home phone, microwave, wireless video transmitter, AND worst of all the wireless network hubs.

These thing sometimes totally block out the XM signal if you are close enough to their source.

First, the signal strength indicator does not directly display the actual amount of power being received by antenna. Like the Sony PNP, It more likely displays quality of the decoded signal based upon BER. A weak signal has more errors and for the SkiFi, is indicated by a low number of "bars" being displayed. And a strong signal with no or few errors is given the full strength indication.

There are 2 likely causes why yours radio shows no satellite signal when you have a clear view of the southern skys. The first, is local interference. There are good many sources that can easily "jam" the XM satellite signal. Since the display indicates BER and not received energy, the satellite shows a total loss of signal. If the terrestrial signal is strong enough to overcome the interference, you continue to enjoy XM without dropouts. The terrestrial signal is also on a slightly different frequency and may not be subject to the same interfering signal.

The other cause is a little more interesting. Almost all modern receivers have some method to prevent overloading the RF section of the radio. This usually done by some form of automatic gain control, AGC. If you happen to drive near the site of the terrestrial repeater, the receiver's AGC starts to decrease overall sensitivity to prevent overloading the RF stages. At some point the gain is decreased so much that the satellite signal can no longer be detected.

hope this helps