On 8/16/2011 6:12 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.
The azimuth pattern will be much the same over ground. If you
vertically stack antennas very close together you can see interaction
between the antennas that can degrade the azimuth pattern. Although it
might improve the elevation pattern (the useless lobes that can cause
noise pickup from under the antenna). However if you don't have fairly
flat ground IMO modeling over ground may or may not give you accurate
results unless you have a program that compensates for the local terrain.
> 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.
The first two sets of number were only two antennas to show the
effects of vertical and horizontal stacking. The third set of number was
the 4 stack.
73, Jay K0GU
> 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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