Bad reception/snowy pictures/digital breakup/pixelation is quite often caused by low grade - Premade/molded fly leads (typical white antenna cords). They have limited life and durability due to low grade cable and poor plug connections. We install antennas and home theatre and never leave without replacing the antenna calbe/fly lead. We always see improvement because the cable beyond your wall plate is equally important to the lead to your television!
DON'T SPOIL YOUR SIGNAL and install a low grade cable from your wall to TV, this cable makes sure that you have the best picture your TV can get from the wall socket because the cable standard is above what most installers fit into your house.