Hi Mono and all,
Yup, not all and in fact rather few "general coverage" antennas receive 800MHz well, when you try to cram 10lb of crap into a 5lb sack you have what's known as a blivet. That's just my way of saying when you try to make something do too many things something's gotta give.
I solved my problem by combining signals from an Andrew 3dB gain 800MHz cell phone antenna with those from my main through a diplexer but there's more than one way to skin a cat. The point is the only antenna that does really well is one designed for the band, not some blivet antenna.
Still I'm puzzled why the NJSP tower in Dover Twp. is weak while the NJT tower in Newark is about the same strength and it's several times the distance. There might be some obstruction, multipath cancellation or something, I haven't exactly done a site study to suss it all out. The antenna system works just the same and that's really what matters, the main is deaf on 800 so I went looking in the hat and found my rabbit.