XM repeater locations?

[kvahey@comcast.net]

Does anyone have an idea on how many repeaters XM is using in the Boston area?

I am curious because terrestial service seems poor in Boston compared
to the Chicago market. I use one of the portable units and I have
noticed it is very hard to get a good signal in the Back Bay and
Cambridge at times . However I get a very strong land signal in the
Chelmsford area.

Also as a general rule what is the expected coverage area of each repeater?