On 9/4/2021 8:19 PM, Lux, Jim wrote:
On 9/4/21 8:05 PM, Wes wrote:
For an illustration try this:
http://www.cuminglehman.com/wp-content/uploads/Introduction_to_Antenna_Test_Ranges_Measurements_Instrumentation.pdf
and look at the figure on page 4. This shows the usual antenna range
situation where the test antenna is receiving a signal from a point, or small
aperture source. This is how I would run this comparison. I think, but do
not know for sure, that I would use the larger dimension of the vertical(s)
as the "D" in the equation. The idea is to have a plane, or near plane, wave
over the whole aperture of the test antenna in both directions. Note that
some antennas, Yagis for instance, can have an effective aperture larger that
the physical aperture.
Wes N7WS
But that's the 2D^2/lambda - and that comes out strangely small. And it's
not effective aperture (that's more about voltage/power at the feed) - this is
about the physical optics.
D =30m (across the 4 square diagonally) is almost certainly bigger than the
height of the 80m elements (20m?)
Sure, that's what I said. There are two test cases, 1) a single vertical and 2)
four verticals. The four verticals may, or may not, have 1/4 lambda spacing and
they could be shortened, loaded antennas. Pick the largest physical dimension.
Wes N7WS
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