See http://www.tvtechnology.com/digital-tv/0148/does-dtv-interference-from-taboo-channels-exist/214566
A consumer modulator on UHF 63 puts junk on 62-64. Junk on 64 is probably what killed my reception of UHF 50, 50 + 14 = 64. I thought it was stupid, but with the modulator on, 50 either...