Thanks Rabbit.
UPDATE:
For several days now PBS (21) has been edgy -- audio breaking up, slight pixelation. It has been probably my strongest signal; have never had a problem with it since 2011 when I installed my present system.
So I put the new box thingy in that goes under the antenna (that the coax screws into) that I bought last winter. Didn't help at all.
So I started rotating the antenna. One way, no good. Went the other way and it's coming in fine, along with the other channels.
I'm thinking I should probably put a rotor on it, so I can compensate for what I assume are slight changes in the atmosphere, weather, seasons, etc. that are causing my occasional problems. Tweaking it from the living room seems a lot better than crawling up on the roof and having the ladder blow down like it did last December.
Thirty-some years ago I had a rotor, but after a while it would mess up and not work right. It ended up being a big PITA so I didn't use it anymore and eventually took it down.
I'm assuming today's rotors are much better . . . ?