Quote:
Originally Posted by MisterMe
... We know that trees block UHF, but I have read no post or link on this forum why this is the case. We also know that trees attenuate VHF, but they do not block it all together. Many tree leaves are about the same size as the elements of a UHF antenna. Somewhat like an antenna, green leaves extract the energy from UHF and send it to ground. VHF is much longer wavelength for which tree leaves do not act like an antenna.
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Regarding UHF, block may be too strong a term. UHF frequencies are attenuated more than VHF, but less than microwave frequencies when passing through vegetation. Water molecules (rain, snow, vegetation, etc.) are excited by RF. Energy is dissipated as heat. Yes, trees are grounded, but the attenuation will still occur if a tree were isolated from ground The phenomenon is more pronounced as frequencies increase which is why microwave ovens operate at 2.4 GHz rather than VHF or UHF frequencies.
Given the predicted signal levels, vegetation attenuation does not explain complete loss of signal on all but two channels (IMO).