I am having a problem with my ota hd channels. Everything below channel 19 has sound but everything above gets sound for a split second and then cuts out. I have very strong signal strengths on all my channels. They are virtually identical in the hundreds on my stb on all six of my digital channels. I have changed my antenna. I have tried this on a samsung hd receiver and on my dish 921. The only thing I haven't changed is the cable.Any help would be greatly appreciated.Frustrating!