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Trees - More



Franklin Antonio asked for technical references re trees attenuating RF.

I have now found the reference (tnx GM4ULS) in the RSGB Book "HF Antennas
for all Locations"; by Les Moxon G6XN; 1982 pp 141 and 194.

The effect of obstructions:
" If the object is a conductor, a current is induced in it and this in
turn sets up its own field so that energy is re-radiated. (some of this
might go in the required direction in the correct phase but, on average,
represents wasted power from the tx).

"Horizontally polarized antennas can usually be more or less buried in 
trees with little or no ill effect.

"A single row of trees at 30-40ft from a vertical antenna had little effect
but 50 yards of thick woodland caused several dB of attenuation at 28 MHz.

"Under the same conditions no attenuation was observed in the horizontal
case."

(Goes on to suggest the use of woodland to achieve low angle radiation from
verticals by attenuating the reflected wave so that it no longer interferes
with direct wave from an antenna at tree-top level.)

(smug grin) Nice to know my memory didn't fail me this time. 
Makes a change from usual ;)

73
Richard W L Limebear G3RWL
g3rwl@amsat.org
FOC # 1188

          So many beautiful girls ..... (sob) so little time
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