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So the trees really are that big an issue, huh? I was hoping being 5 miles away from the towers would make this a piece of cake.
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I wish it were that easy. Sometimes it is, other times, it isn't It's a real-life example of Forrest Gump's mother's box of chocolates.
Several springs ago, I paid a visit to a visit to local viewer whose home was in the Affton area of St Louis county. If you look up Affton on the TVfool map, you'll see it's within a triangle formed by a number of the St Louis towers, most within 3 miles and visible to the naked eye if not for trees and surrounding homes. The trees were already in full leaf and it was a windy day. On my spectrum analyzer, I could see as much as a 30 dB reduction in signal power just by moving a dozen yards from where the tower was visible to where I was behind one of those mature silver maple trees. When the wind gusted, I could see notches as deep as an additional 20 db within the channel bandwidth. I've observed similar behavior at other tree-bound locations, so this wasn't a unique observation.
Now you can see why I'm so pessimistic that through-the trees reception is so apt to be unpredictable, especially with weak UHF signals.
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Can you explain multipath?
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Multi-path occurs when:
1. There is some signal that, besides taking a straight line of sight path to the receiving antenna, also reflects or diffracts off other objects before arriving at the antenna at a slight time delay relative to the original signal.
2. The LOS path is blocked (hill, tree, building, etc) and the only signals that arrive are some chaotic mess of signals that are some combination of reflected and diffracted copies of the original, perhaps with some remnant of the original signal at some level of attenuation.
It's generally up to the tuner to try to sort out the mess and reassemble something that decodes well enough to be usable without excessive errors. When the error correction circuits get overwhelmed, there will be a visible defect in the video or an audio defect ranging from a minor blip in either up to a pixelated mess to a complete loss of any audio or video, depending on the severity of the signal impairment.
Ken Nist, on his website at
http://www.hdtvprimer.com/ANTENNAS/fixes.html and
http://www.hdtvprimer.com/ANTENNAS/siting.html sums it pretty well.