W7GJ'S 6M YAGI 70' HIGH
The following E and H plane charts show the pattern
and gain (including theoretical ground gain effects) of the 6M35WL as installed
at 70' height at W7GJ. As the antenna is elevated, the vertical pattern
rapidly begins to resemble the E plane pattern, with a broader main lobe
having 14 dbd "free space" gain - the same gain as the third vertical lobe
(at 20 degrees) when the antenna is pointed at the horizon. As a
result, there is not much difference in shorter Es signals (with
higher incoming angles) as the antenna is raised up to about 20 degrees.
(However, as the antenna is elevated, there is very quick reduction in
the low angle ground gain, which substantially reduces/eliminates local
RFI in any particular direction).
For more distant stations with lower incoming
propagation angles (such as ground wave, troposcatter or double hop Es),
the maximum gain of the lowest lobe (when the antenna is pointed at the
horizon) is clearly beneficial. Pointing the antenna at the horizon
to obtain the approximately 18.5 dbd gain from the second vertical lobe
at 12 degrees elevation has also proven advantageous in EME communciations
when the moon is at that particular elevation. In addition, the large
gain in the higher lobes is definitely desirable at this location - surrounding
mountains create a high horizon in certain directions,
totally blocking signals coming in at lower angles.
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Thanks to VE7BQH for providing the above antenna pattern plots.
