On 8/16/2011 9:54 AM, Jay Kesterson K0GU wrote:
> 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.
VE7BQH's information also uses free space designs since EME generally
involves elevation above the horizon. Some can argue that HF use is
better served by a more narrow but taller array which would create
a broader main lobe and addition lobes in the vertical plane (more
choices of take off angle) while others will argue for an H-frame
that is exactly 1/2 wave high since it minimizes the up/down lobes
and results in a "cleaner" pattern (fewer vertical lobes).
73,
... Joe, W4TV
On 8/16/2011 9:54 AM, Jay Kesterson K0GU wrote:
> 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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