> 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.
73,
... Joe, W4TV
On 8/16/2011 8:12 AM, Pete Smith wrote:
> But....
>
> When modeling a vertical stack, it is important to include the ground in
> your model. Free-space modeling does not take advantage of ground
> reflection. X/2X/3X spacing is a standard (where X is the distance from
> ground to the bottom antenna), and seems to give a nice clean pattern.
>
> 3 dB seems like an awfully small advantage from the mechanical
> complexity and wind load associated with an H-frame. Someone also wrote
> that a multi-antenna vertical stack could not produce the desired 10
> degree takeoff angle. Based on modeling, I don't see why this should be
> so, so long as you have the ability to switch in different combinations
> of antennas.
>
> 73, Pete N4ZR
>
> The World Contest Station Database, updated daily at www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com,
> spots at telnet.reversebeacon.net, port 7000
>
>
>
> On 8/15/2011 10:30 PM, Brobakken, LA6FJA K3RAG wrote:
>> THANKS FOR NICE MODELLING!
>>
>>> From my HTC, LA6FJA
>>
>>
>> ----- Reply message -----
>> Fra: "Jay Kesterson K0GU"<k0gu@verinet.com>
>> Dato: tir., aug. 16, 2011 03:36
>> Emne: [TowerTalk] H frame for 10 or 15m
>> Til:<towertalk@contesting.com>
>>
>> On 8/15/2011 1:30 PM, Stein Roar LA6FJA-K3RAG wrote:
>>> Hi
>>>
>>> does anyone have ideas sizes for a H frame for 4-5 el yagies for 10 m and
>>> 15m ?
>>> is it 1/2 wl , 3/4 wl or 1 wl spacing ??
>>>
>>> I saw one from http://www.arraysolutions.com/Users/h2a.jpg Arraysollution
>>> from PY5EG
>>>
>>>
>>> 73 LA6FJA Rag
>> Your best bet if possible is to model the antennas and look at the
>> gain compared to one antenna and the patterns. The wider the horizontal
>> spacing the bigger your first side lobes. That may not be a problem if
>> you can't stack them very far apart horizontally. But if you can stack
>> them far apart then you need to possibly chose a bit more gain vs a
>> better pattern.
>>
>> I have a model of a Hy-Gain 105CA (24' boom) for my antenna modeling
>> program. And I am a bit bored so here goes...
>>
>> Just to get the feel for how the horizontal and vertical stacking
>> distance affects the antenna I first model only two antennas.
>>
>> Single 105CA = 8.24 dbd
>>
>> Two 105CAs stacked vertically spaced
>>
>> 20 feet = 10.50 dbd
>> 24 feet = 10.84 dbd
>> 28 feet = 11.12 dbd
>> 32 feet = 11.30 dbd
>> 36 feet = 11.35 dbd
>>
>> As far as vertical spacing is concerned somewhere around 24-28 feet
>> looks pretty good. There is less interaction between the antennas as the
>> stacking distance gets larger. More than 28 feet produces little
>> advantage and a fair amount of extra wind load..
>>
>> Two 105CAs stacked horizontally spaced
>>
>> 20 feet = 9.72 dbd (first side lobes are ~37 db down)
>> 24 feet = 10.27 dbd (first side lobes are ~30 db down)
>> 28 feet = 10.66 dbd (first side lobes are ~22 db down)
>> 32 feet = 10.95 dbd (first side lobes are ~16 db down)
>> 36 feet = 11.11dbd (first side lobes are ~16 db down)
>>
>> This will depend on how much you value gain compared to pattern. I
>> would likely choose 28 feet vertically and 24 or 28 feet horizontally. I
>> like a nice tight pattern. Not a lot of advantage beyond 28 feet.
>>
>> 4x H-Frame array of 105CAs spaced
>>
>> 20' high - 20' wide = 12.00 dbd
>> 20' high - 24' wide = 12.46 dbd
>> 24' high - 24' wide = 12.71 dbd
>> 28' high - 24' wide = 13.09 dbd
>> 28' high - 28' wide = 13.53 dbd
>>
>> The first azimuth side lobes are essentially the same value on the 4
>> stack as the 2 horizontal stack. This model is based on a 24 foot boom
>> 10m yagi. A shorter boom will require a bit less spacing and a longer
>> boom more spacing.
>>
>> 73, Jay K0GU
>>
>>
>>
>> _______________________________________________
>>
>>
>>
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>>
>>
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