70 over 2 stacking distance?

[VK4GHZ]

Hi all

How high above a pair of 2M12's do I need to go to mount a 432EME12?

My hazer trolley is only so big, and the bearing above the rotator is less than a metre to begin with.
The 11 feet separation (as per M2 recommendation) between the 2M12 is manageable, but another 11 feet above that again, is not!

So, can anyone suggest a suitable minimum height above a pair of 2M12's I should mount the 432EME12?
I don't mind some compromise in the 2m stack, but obviously, if it starts to negate the benefits from stacking too much, then there's no point to adding a second 2M12.


Suggestions?

[VK5APN]

Adam

There are a couple of good web sites worth a read.

http://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm

And the best one that deals in stacking different band yagi's is

http://www.directivesystems.com/STACKING.htm

What I would do is place the 70cm yagi right in the middle between the 2m yagi's if pole extention is a problem. A compromise but probably better than other arrangements.

Hope this helps and Good Luck with your new yagi.

Regards

Wayne
VK5APN

[VK2KRR]

Adam,

I've been working a lot with yagi spacings lately.

1.32m between those two 2m yagis, is that the correct spacing? From what I've read it should be at least 3m.

There is no real minimum, depends on how much compromise u can make. I'd probably go 1/2 the stacking distance of the 2m yagi and put it there, which in my mind would be 1.5m. I think it would work fine.

[VK4GHZ]

Thanks Wayne & Leigh.

Both of those URLs are very informative, especially the second one - Thanks Wayne.
Simple, to the point, with clear graphics.

Leigh, an error in the graphic, and you're correct.
The correct stacking distance for a pair of 2M12s (as given by M2) is 11 feet, 335cm... must have had a brain fart when attempting to fix the graphic above!

The first response to the question from M2 was:

Being the third harmonic of 2m, as you can imagine there will be some interaction between the 2m antennas and the 432EME12 with the 432 antenna placed in the middle of a phased array.
Without spending several hours modeling, it’s hard to say with certainty if there is a combination that will allow it.
The 432 antenna should be mounted outside that stack.

Jason then followed this up, and advised

Hi Adam,
It always pays to get a second opinion.
I’ve run this by K6MYC and based on his experience, interaction between the 432-12EME and the 2M12 stack should be minimal with the 432-12EME exactly in the middle.
I hope that simplifies your stacking arrangement!

Given Mike Stahl's background and extensive experience with antennas (the "M" in "KLM", and founder of M2 Inc), that's good enough for me.

Mounted outside of the stack, the 432EME 12 would be placed above the pair by:
= ½ x 2M stacking height + ½ x 70cm stacking height
= ½ x 335cm + ½ x 137cm
= 236cm

[VK4GHZ]

Actually, one thing that comes to mind, and I have just sent M2 one last question;

Your recommended stacking distance for a pair of 2M12s is eleven feet.
Mike suggests the 432EME in the middle of that would be ok.

What if I were to spread the 2M12’s out a bit further than the 11’ (say, by another 12-18 inches), with the 432EME12 still in the middle?
This should reduce the 2m “area blockage” caused by the 432EME12.

Or would spreading the 2M yagis apart beyond 11’ have an overall detrimental affect?

Stacking distance discussion you find on the internet generally refers to minimum stacking distance.
I'm keen to hear M2's response on this.

At which point does increasing the separation distance become detrimental?
Whilst waiting on M2, does anyone have any experience with this?

[VK2KRR]

Adam

You can use the 1/2 the 2m stacking + 1/2 the 70cm stacking at your quoted 2.36m. If its outside your 2m stack, this means the mast will need to be at least 5.7m long outside the top of the tower, then u also need length inside the tower to reach the rotator.

I quoted before the 1.5m as 1/2 the 2m stacking distance and put your 70cm yagi there. If u look on the Directive Systems Yagi stacking page, in figure 4 u see 'stacking with some penalty'. As it says, band 1 will have a minor reduction in performance. My suggestion was to go a little further back out have the 70cm yagi just at the edge of the 2m aperture. There may be a minor reduction in performance but I doubt you would notice it. This would make ur mast about 4.8m out the tower. My new one is about this length.

To your other question, if you start increasing the distances to much you would probably lose the sharp pattern and end up with bigger side lobes, just a guess really. Good idea though, see what they come back with in answer to ur question. Though moving them say another 150mm wider probably wouldn't matter a great deal.

[VK4GHZ]

Mounting the 70cm yagi above the 2m stack isn't an option for me, unfortunately, due to mechanical limitations.
So it has to be within the 2m stack, or not have a 2m stack at all, and just mount the 432EME12 at full recommended distance above a single 2M12.

[VK3QI]

Adam,

We had an extensive discussion of the issue starting back on June 30 under the topic Antenna Interactions.

It might be worth re-reading the discussion. David VK3AUU might be able to lend some insight into your particular issue.

Cheers

Peter VK3QI

[VK3ZAZ]

Antenna inter-reaction is always a compromise otherwise we would need multiple towers or poles all over the yard which is impractical and unsightly.




From internet




STACKING DIS-SIMILAR YAGIS

One of the most asked questions about antennas today is "How should I stack all these VHF antennas on my tower?" The problem is that most hams are lucky to have one tower and then they try to stuff antennas for ten VHF/ UHF bands on that same lone tower. Hanging several wire antennas off the heavily loaded structure is typical as well. So how do you plan such a setup? The answer may be found by looking at a few spec sheets and making some simple calculations.

First we need to understand a few things about antennas. Every antenna has a collecting area to snag errant electromagnetic waves. It is no accident that signal strengths are measured in microvolts per meter. The truth is that a larger antenna can intercept more energy by simply occupying more physical area. Sounds simple enough! This is also the reason that apparent path loss goes up with frequency. At higher frequencies, the antenna is smaller and cannot collect the same amount of energy that it's lower frequency sister antenna does. The collecting area of any antenna is called its aperture. Generally, the aperture of most amateur VHF directional antennas is larger than the physical frontal outline. Yagis have a much larger aperture. Arrays of half waves, such as collinears, have smaller apertures extending just beyond the physical structure, while parabolic antennas have apertures that are slightly smaller than the physical size of the dish.
If an antenna is sited on a mast, as long as nothing is located within the aperture area, that antenna will function normally. If you are stacking two antennas for more gain, you should align the antennas so that their apertures just touch. This produces a maximum gain effect. The two apertures have merged into one big aperture with twice the square footage or frontal area of a single antenna. twice the area means a 3 dB increase. You can stack antennas in both vertical and horizontal planes. A typical DX arrangement for a high gain antenna system is a quad array, or four stack array. It combines multiple antennas in bith the e and h planes, as seen below. Note that the apertures are just touching. If they are overcoupled with smaller stacking distances, the collecting ability is reduced, but sidelobes will be reduced as well.
We try to provide suitable stacking distances for all of our antennas. This information is always printed on the specification sheet for the individual antenna. For horizontally polarized antennas, the vertical stacking distance is referred to as the h-plane or magnetic field plane. The e plane or electric field extends out along the axis of the elements. In the case of horizontally polarized yagis, this would be the side to side stacking dimension as shown above. Loop yagis are slightly different in that you have no linear rod elements, but the same rules apply. You can see from the figures, that the stacking distance is exactly the diameter of the aperture. One half of the stacking distance is the apparent radius of the aperture. Note also that, for yagis, the e plane aperture is slightly wider than the h plane dimension.
So how do you arrive at a proper spacing number for different bands? If you are stacking two antennas on different bands, you must look at the stacking distance for each antenna and locate the antennas so neither aperture sees the other antenna aperture. Let's take an example. We wish to stack a DSFO144-12 along with a DS222-10RS on the same mast. The 144-12 stacking distance (h-plane) is 10 ft 8" while the DS222-10RS is 74" . Take half of the stacking distance for the lowest frequency antenna and you have the extent of the aperture boundary for that antenna. In this case it is 5 ft 4 inches, or 64". Do the same for the other antenna. The correct distance for zero interaction, then, is 64 plus 37 inches, or 101" total spacing. Simple enough. There is no way either antenna will be bothered by the other PERIOD!


A simple test is to set up test antenna and run metering cables back to the receiver like they do in Fresno on their roof top.
Pump in some rf and adjust the spacing to see what happens.

[VK3QI]

Adam,

If you go through all the previous discussion on this topic, check out the previous cited documentation and look at the results that David VK3AUU did via computer analysis, the ONE KEY finding is the following:

As anti-intuitive as it seems, the placing of the 70cm antenna within the stacked 2 metre beams (your requirement), affects the 2 mx beam pattern much more than the 2 metre beams affect the 70cm beam pattern.

The wider stacking of the 2 metre beams is far preferable to the closer stacking recommended by some proponents, especially when a 70cm yagi (or yagi stack) is implemented between the 2 metre antennas.

K6MYC's recommendation that you aim for symmetry in placing the 70cm yagi is sound advice, as this leads to the least pattern deformation of the 2 metre stack.

The original work done on this back in the mid 1980's still stands as the best graphical explanation, which can now be backed up by relatively easy and quick computational models.

Cheers

Peter VK3QI

[VK4GHZ]

A follow up from M2.

Hello Adam,

Going beyond the recommended stacking distance will reduce the overall apparent gain increase.

Regards,
Jason Boyer, N6EY
Amateur Marketing and Sales

[YU7EF]

Adam

From years of experience I can tell you that putting 432EME12 right in the center between two 2M12 antennas will work perfect
and mutual influence is so small that it can be ignored. However, making such model is not difficult so before writing these lines
I created model similar to yours ... Since I don't have M2 data for the model and dimensions shown in the manual include bom
correction, unknown to me, I took some of my antenna models, almost identical in boom length, and checked simulations both
with and without other band antennas

BTW, based on simulations, 2M12 optimum vertical stacking distance is 3.300m just as recommended by M2 so if you have your
antennas at 11' that is just about right and you should have about 2.9dB stack gain with pair ...

To make it short, by palcing 432EME12 in the center between 2M12 (1.65m from either 2m antenna) there is no difference and
distortion of 2m radiation pattern nor gain loss at all - or hardly can be noticed with magnifier,

70cm pattern shows minor disturbance but nothing that you have to worry about and gain is still the same, actually it is 0.1dB
bigger than antenna simulated alone ...

Now, I must say that these simulations were made using my design (EF0211B for 2M12 and EF7014M for 432EME12) but it is quite
possible that M2 antennas may behave a bit different - I have no experience with them and can't say for certain how they will
behave in same situation and how sensitive they are to objects within antenna vicinity - result might bi different but for sure not
significant so I am confident and sure that such setup will work just fine ...

So just go ahead and put 432EME12 in the center between 2M12 antennas and enjoy it ...

I have all diagrams so if you are interested to see them send me an e-mail and you will have them all - or I can post them here

73, Pop, YU7EF