my tv keeps losing its signal?

my tevion 52 inch tv keeps losing a signal on some channels mostly terrestial channels ie 1 3 4 5 and on most popular channels like sky 1 or disney channel . funnily it does it on sat night busy tv watching time ....tv screen goes blank and sends no signal sign ...it is worse when the colour red is on the screen picture breaks up and goes off intermittently until giving up altogether, help please.!