[donjm27]

This is a wealth of information, everyone. I'll try to consolidate your questions for the sake of efficiency.

- The Radio Shack UHF antenna is too old for me to identify, but each of its arms is about 30 inches long. It's been inside its whole life, so it's in new condition and used to do a good job of bringing in both UHF and VHS stations, both here in Corvallis and in Eugene, back in the analog days and up till recently. I don't think the tuner in my digital Samsung TV is as good as the one in my old Zenith converter box, but both currently have the same problems with the transmitters up on the hill.

- I only have one TV, and the amp is disconnected and put away.
- I've tested my system with several lengths of known good coax (one was tested by an installer just before I rented it), and they all perform the same as the one attached to my house.
- My local channel reception problems predate the purchase of the C5, so I don't think it's an issue.
- The C5 is joined to the Radio Shack UHF using the provided connector. It has inputs for UHF, VHF and a combined output.
- John, I like your idea of getting the UHF stations at 88 and 153 degrees, but since those are both analog stations, I'll keep chipping away at the ones up on the hill (I work practically at the base of them, so they taunt me daily), and use those as my backup. I'll do the clean scan routine that you describe.
- I also think I should be able to get to FOX in Eugene (KLSR- 31), and if I scan with the antenna oriented just so, it gets entered on my list. But it's only one bar on my sorry excuse for a meter, and can't be counted on. A solution for everything might be to get PBS from KEPB- 29 (per John's idea) and reliably reach KLSR with a small UHF antenna under my southeast eave, aimed halfway between those stations. I confess to being too vain and lazy to take the obvious route and put the mast on the roof.
- I agree that the building materials in the attic are a problem, but the sudden onset of this makes me think there's something else happening.
- I'm also unaware of anything else happening in the neighborhood, although my engineer friend up the street did once boast that he could probably sterilize speeding drivers with a microwave transmitter he keeps around for fun. And while he built a Faraday cage in his basement, I don't think he wrapped my house in chicken wire while I was on vacation. I may take off a piece of siding, to be sure.
- Good idea, dkreichen1968, I'll give KOAC a call and see what's up with the weird artifacts.
-GroundUrMast, I'll carry my little test TV and antenna over to the neighbor's to check for a multipath issue in my attic. My narrow attic doesn't let me give me much wiggle room, and happiness may be just a few steps away.

Really, everyone- thanks for the feedback and suggestions. It's amazing that this expertise is out there through your generosity. I'll keep you posted, once I have time to explore a bit more.