Sirius XM radio only works when traveling through a large city

[bbach6]

My Sirius XM radio is constantly in the "acquiring signal" mode except when I travel through a large city like Atlanta. It finds the satellite signal intermittently in Atlanta and works fine for awhile, but then goes back to "acquiring signal" again. Not sure what the problem is, maybe a poor antenna gain. Anyone have a recommendation for what could be the issue? I tried refreshing the signal, but that does not work either.

Thanks.