My modelling for the planned 4x104CA stack is done by EZNEC and HFTA.
I did not write that the vertical stack of 4 yagis cannot provide a desired
10° vertical lobe.
Of course it can by proper combination of those antennas, but it will have
less gain at that angle and a less clean pattern then the H frame stack.
I do have the space on my tower for a 4 high stack on 10m, but would prefer
the H frame stack any time on that band.
[mailto:firstname.lastname@example.org] On Behalf Of Pete Smith
Sent: Dienstag, 16. August 2011 14:12
Subject: Re: [TowerTalk] H frame for 10 or 15m
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
73, Pete N4ZR
The World Contest Station Database, updated daily at www.conteststations.com
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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"<email@example.com>
> Dato: tir., aug. 16, 2011 03:36
> Emne: [TowerTalk] H frame for 10 or 15m
> On 8/15/2011 1:30 PM, Stein Roar LA6FJA-K3RAG wrote:
>> does anyone have ideas sizes for a H frame for 4-5 el yagies for 10 m and
>> is it 1/2 wl , 3/4 wl or 1 wl spacing ??
>> I saw one from http://www.arraysolutions.com/Users/h2a.jpg Arraysollution
>> 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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