I had same problem with Spectrum 8 SP-813. All VHF stations are missing. It acts like a UHF only antenna. It is happened that I also bought a Winegard HD6010 FM Antenna for my FM tuner. When I connect Winegard FM antenna to my HDTV tuner, it picked all HDTV stations listed as green in
Http://transition.fcc.gov/mb/engineering/maps with strong signals. This $20 Winegard FM antenna has two simple dipoles in perpendicular directions make it not directional. I returned Spectrum 813 and cancelled my cable TV service.