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 _________________ Topband Reflector Archives - http://www.contesting.com/_topband
