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If a vertical 28 MHz antenna is surrounded by moderately thick trees that are higher than the top of the antenna signals will be attenuated 2 to 3 dB on average. Tree attenuation with horizontal polarization under the same conditions usually will be negligible. At 144 MHz the same trees will attenuate signals 6 to 12 dB on average with vertical polarization and 3 to 4 dB with horizontal polarization. However, with vertical polarization at both frequencies and with either polarization at 144 MHz there will be large strength variations with small changes in antenna position due to standing waves caused by tree reflections.
