Thanks for your input. To provide more details I have a fringe antenna mounted in a 3rd floor attic and have an inline amp which is used to distribute antenna signals to 2- 722K and a Mits HDTV. My home is about 34 miles from the local area antenna farm, which includes the transmitters for 9 digital channels. Living near the east coast, the terrain is pretty flat. For about 2 years, this system worked without problem until up to about a week ago, when I started to get the wild swings in signal strength on 2 of the 9 channels. This problem has not been consistent during this period. Sometimes, the loss of signal message may not appear in an evening and others it occurs several times a minute plus pixelation, etc. Weather conditions are fine. No storms during this period. There are no new structures in my area to change multipath conditions. There is a nearby water tower, which caused serious multipath problems when watching hi-VHF analog channels but caused no problem with the UHF stations. Now, one of the local stations is using the same hi-VHF frequency for transmitting digital. Before, the change over, I couldn't watch the analog signal but now the digital signal is one of my best channels and is not one of the two I'm having a problem with.
I don't believe this problem is caused by multipath, but some other transmission anomaly. Plus the Mits HDTV is not affected by the condition.