On 2/29/2020 9:56 AM, Guy Olinger K2AV wrote:
Have to disagree on the no-use-for the horizontal leg.
It fills in the doughnut hole in the high angle radiation, which in
contests is very good for keeping others from planting on your run
frequency. Also there are high angle path opportunities that are gradually
becoming more recognized.
This effect is not nearly as great as generally believed, and depends on
the relative lengths of the horizontal and vertical sections. For
example, consider an L with 70 ft and 70 ft sections, as compared to 100
ft vertical and 35 ft horizontal. the difference in field at 70 degrees
elevation between the two antennas is 4 dB over Sandy soil, 3 dB over
Very Good soil. For 50 ft vertical and 80 ft horizontal, the difference
is 4 dB over very good soil as compared to 100 vertical, 35 horizontal.
The reason for the difference, of course, is the current distribution
between the two sections depending on their electrical length.
Comparing a T with 50 ft vertical and 55 ft horizontal to an L with 50
ft vertical and 85 ft horizontal over Very Good soil, the difference is
also 4 dB.
These differences are less than an S-unit, hardly enough to prevent
someone poaching a run frequency. Propagation for shorter distances
corresponding to a higher wave angle are covered by ground wave on 160M.
The way ARRL and NEC plot vertical patterns can be deceiving, because
they always set the peak of the pattern to full scale. To see the
difference, one must plot both antennas with the same scale. In NEC,
this is accomplished by modeling each antenna, displaying the vertical
pattern and saving the traces, then recalling the saved trace for the
other antenna and selecting the recalled trace. The cursor can then be
moved along the vertical axis and will display the difference in dB
between the traces.
There are many examples of this technique in
http://k9yc.com/AntennaPlanning.pdf
A shorter vertical sections reduces the radiation resistance, which
increases losses in the counterpoise/radial system, which in turn
strongly depend upon soil quality.
73, Jim K9YC
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