On 8/16/2011 7:17 AM, Joe Subich, W4TV wrote:
> > 3 dB seems like an awfully small advantage from the mechanical
> > complexity and wind load associated with an H-frame.
> The advantage of an H-Frame ranges from somewhat less than 5 dB for
> systems with less than optimum spacing to slightly more than 6 dB
> with maximum gain spacing. Without doing the modeling, one can
> look at the material by VE7BQH (http://www.vhfdx.info/VE7BQH6.html)
> for six meter antennas. The spacing information for the 5 element
> antennas with 0.75 and 0.76 wavelength booms provide a good range
> for 10 meter antennas like the 105CA (scale the table values by
> 1.75) and the information for the ~0.6 wavelength booms would be a
> good starting range for 4 element yagis.
Just take into account that VE7BQH's fine antenna array information
is a maximum gain design for EME. The first side lobes in the azimuth
are only down around 12 db from the main lobe in many of those
calculations. If you can live with -12 db first side lobes then the
spacing is fine. If not the horizontal spacing needs to be reduced a bit.
BTW I made one error in my chart. I show the first side lobes on the
horizontal stack at 36 feet wide to be 16 db down from the main lobe. It
actually is ~13 db down.
Two 105CAs stacked horizontally spaced
36 feet = 11.11dbd (first side lobes are ~16 db down)<<< Should be ~13 db down
73, Jay K0GU
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