Hi-Def Antennas

I just had VOOM installed and it works great on the dish signal but the piggybacked what looks like a Terk bar type antenna for the off-the-air channels. I have called several times because I'm getting pauses in the sound, pixilization (digital anomolies) and total loss of signal, mostly on KNBC and KABC (who is, unfortunately, multi-casting on their bandwidth) and sometimes on KCBS. Channel 5 (who I understands loans antenna service for KNBC) comes in great with no problems. That's KTLA but I don't remember the network. KCET, LA's PBS station, is also okay with few low signals. I use the "re-aim off-air" antenna often and it does some good. My question, after shopping online for other antennas and having marginal luck, is does anyone have any info on hi-def antennas which are good for 80 miles ?(my approximate distance from Mt. Wilson). I guess I might have to call a local service shop and find out about changing the antennas.

BTW, when I had cable, these same channels had some dropout and loss of service so I'm inclined to believe these stations just are not technologically up-to-date sending out over-the-air hi-def signals (which could be their satellite signal). Cable also picks those channels up with an antenna.