On 3/3/2018 11:29 AM, dl8yhrfrank--- via Topband wrote:
Hi everyone...
Did annyone has experience in using more wide spacing the 8 circel rx
arrya?
Im running the hiz 8a lv2 160-2 arrya in a 200 foot spacing in the fields on a
litel hilltop away from
A very simple analysis is as follows:
Imagine a 4 element rectangular array: end-fire/broadside.
In the broadside case, the beam width decreases as the
spacing increases. However, once you go past 5/8 wavelength,
sidelobes appear. Thus in some sense 5/8 wavelength is
the optimum for the broadside dimension.
For end fire, the beam width is nearly constant up to
1/8 wavelength, but the gain increases with increasing
spacing. Beyond 1/8 wavelength, the beam width gets
considerably wider. Thus in some sense 1/8 wavelength
is the optimum for the end fire dimension.
If we now take our optimum 1/8 by 5/8 wavelength
4 element rectangular array and fit it
to a circle, we find that it is almost a perfect fit to
a circle of 16 elements. IOW, you drive four elements
at a time, but have 16 directions to select from.
The size of the 16 sided polygon is 5/8 wavelength
across the flats. The diameter is 2% larger than
5/8 wavelength. This results in a 0.637 wavelength
diameter circle, which works out to 342.6 feet or
104.4 meters for 1830 kHz.
Now if you only have 8 elements in a circle, you have
a compromise. If you want to optimize the broadside
component of the pattern, you need 5/8 wavelengths
across the flats, which results in a diameter of
0.676 wavelengths which works out to 363 feet or
111 meters. This will result in excessive end fire
spacing. Smaller diameter circles with 8 elements
would have better end fire patterns in exchange for
a suboptimal broadband pattern component.
Thus it may be the case for 8 elements, four driven,
that 200 feet is just as good as 300+ feet. You would
have to model it.
Another issue is it is entirely possible to get beam
widths that are sufficiently narrow that 8 directions
are not enough to avoid directions that are several
dB down. This is another reason why a large circular array
really needs 16 elements. And why an 8 element array
should not be made too large.
The Hi-Z array drives all elements, not just 4, so it
is a more complicated analysis.
Rick N6RK
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