It isn't really possible to give a sensible answer to this question because - it depends? (Things like the gain of the aerial, where you are in relation to the transmitter, how long the coax, etc.)
The best way to do this is to fit a powered distribution box as close to the aerial as possible and then run coax from it to the TVs.
BTW, in spite for what some installers may tell you, there is not such thing as a 'Digital Aerial'.
T
April 2010