I use greater spacing than has been described in this thread. (30' for 24'
boom 5el 6m antennas and 50' for 7el 48' boom 10m antennas) The forward
gain is higher. Why should I worry about the side lobes? (I am a
contester.)
Chuck W5PR
----- Original Message -----
From: "Joe Subich, W4TV" <lists@subich.com>
To: <towertalk@contesting.com>
Sent: Tuesday, August 16, 2011 9:34 AM
Subject: Re: [TowerTalk] H frame for 10 or 15m
>
> 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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