Depending on the exact frequency you're looking at, you'll lose about 1 dB every 20 feet with RG6 cable.
If you have even decent signal strength at the antenna, you're going to be fine. I have a passive attic antenna that runs from the second floor attic to a distribution panel in the basement. Each splitter output is about -10 dB, and those run anywhere from 15 to 50 feet to their final destinations. I installed thinking if I needed a preamp for the attic, I would put one in, but turns out I don't.
Hefe's a cruel man, but fair.~edhara
That hefe, he's really smart!~Fish Man