Firstly you need to find out exactly where your TV towers are and ensure that you have you antenna pointing directly at it. Their are Digital Antenna available that are meant for Digital TV. So I am trying to get your situation if I have it wrong please correct me you are not using your digital HD tv for reception and are using the Set top box for your tv reception. The duplicates are like place holders for the various channels so they can justify having the channels to the government so if in future they want to add more content they have the channel to do so. Is the STB a HD one as well because if it is SD it will only have the sound for the HD channels and not be able to display the HD picture. If you have picture going blocky with small cube shaped distortions and crackly sound this is the digital equivalent of the static in analogue meaning you don't have a good reception area. Some how you need to determine the direction of the TV broardcast stations to ensure you have your antenna pointed the correct direction. Hope some of this is useful to you
