Greetings All:
>> Since time immemorial conventional wisdom has it that trees do not
>> interfere with radio. This is what the ARRL has been putting in the
>> books for years, and this is the way it should be.
and
>I really haven't seen much one way or another in except in
>microwave discussions. Lewallen (W7EL) and I have discussed
>this at length, and we both concluded there was no real data one
>way or another.
OK the above represents the common wisdom, I tried an experiment. My
experiment was at 138.83 kHz listening to DCF39 in Germany from Eastern
Ontario, Canada.
Early last year I started listening for this station just above the amateur
LF assignment. Getting out of the old mode comes hard, not listening but
watching with DSP. After the first few weeks this station was visible every
night, the range of the received signal level is over 50 dB - from just
barely visible as a frequency line on the screen to speaker level and I can
hear the FSK bursts that turn ON and OFF water tanks and street lights in
Germany.
By January 2001 I was hearing this German signal over the North Atlantic the
best yet with a 3000 ft wire laying on the ground. My reference antenna was
a 30 ft long, 20 ft high, with the bottom wire 10 ft above ground, resonant
loop. southwest support is a pine tree, 15 ft behind the vertical wire, the
northeast support, 20 ft away, is an English Poplar, some people call this a
deciduous weed. The front tree tops out at 80 ft high.
The long wire on the ground was winning, by as much as 10 to 15 dB.
My suspicions kept mounting about the loop, A gift of another role of RG-59
coax and I had a new opportunity. I mounted a second identical loop (the
resonating capacitor was only 200 pf different)and now I was using a wooden
pole for the back support and the front support was a light metal TV mast,
with guywires by propylene.
The difference between the two loops was amazing. Both were identical
bandwidth, down 6 dB at + and - 1.4 kHz, and local noise levels were only
occasionally measurably different. DCF39 was consistently within my ability
to measure difference in levels, realistically about .6 to .8 dB on both the
long piece of wire and the loop.
The only difference was the support structure, the preamps were interchanged
(same design however). At that point I was using a W&G selective level
volt meter as a receiver, it had excellent gain management under actual
test.
Do trees make a difference, you bet they do.
Larry
VA3LK
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