That's what the WPVI 6 e-mail people told me.
I got analog 6 snowy but watchable on the SAME antenna just before the switch occurred. I also got WPVI-DT on the UHF channel at over 90% signal strength. Now I get 41% signal strength and it fails to lock.
I honestly don't think it's an antenna problem. I have a VHF/UHF antenna that when I rotated it I could pull in both NYC and Philly stations on the old analog VHF frequencies. I can't get any signal from the "new" WPVI-DT signal at all. ALL other Philly and even Atlantic City are coming in above 60%. There is interference or something with WPVI's signal.