Vizio 46" LCD

Question

When I watch digital air channels with rabbit ears the tv go to standbye after a few minutes.I turn it back on and it will shut off again.this happens 2 or 3 times then it will stay on.It only does this on antenna.it works fine on component and s-vid.I thought it was the antenna so I tried several different antennas nothing worked.I returned the tv to the store and they replaced it with a new one and it does the same thing.what could be causing this if not the ant.?