Does anything work? meaning do you get channels to change and can you hear music?
In my opinion, if you unplug the antenna, then the device (xm/sirius direct unit might be bad) OR there is a problem with TT and its connection to the unit.
I would also be sure to open a support ticket on the TT website.
- BTW - yes, my signal meters work on my XM PCR unit that connects to my computer.