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Re: Topband: 8 circle: DXE vs Hi-Z

To: "Lee K7TJR" <>, "'Bob Tabke'" <>, <>
Subject: Re: Topband: 8 circle: DXE vs Hi-Z
From: "Tom W8JI" <>
Reply-to: Tom W8JI <>
Date: Tue, 16 Dec 2014 07:51:45 -0500
List-post: <">>

We probably will just have to disagree about this.

From my viewpoint, the behavior isn't too much different than a big yagi
stack or other antennas we are used to.

The size of the array generally sets the directivity limits. We can add more elements that are closer-in than optimum, and that can certainly help if the size is smaller than optimum, but the trade is gain or pattern cleanliness and sharpness for size.

The forward two elements and back two elements are too close to contribute broadside pattern, which is what provides the clean pattern absent major side lobes in the full size 8 circle. As a matter of fact, adding them in destroys some of the broadside directivity.

If, however, we make the array so small that it loses broadside pattern multiplication, then we can see an increase in directivity through the small endfire length increase.

A .327wl radius array gives about .25 wl endfire spacing in the primary cells (the center elements), and is not improved in pattern quality by adding the forward and rearward cells. The two forward pairs and rearward pairs are not only too close to have broadside pattern contribution, they are closer endfire. They are about 75% of the endfire spacing in the central quad, and nearly 40% of the broadside width. They certainly can contribute endfire, but they actually remove broadside directivity in the process!

In an optimum size array the amplitude ratio from the primary quad has to be 4:1 or 5:1 or more to prevent some pretty significant pattern null area deterioration when the additional 4 elements are added, because they deteriorate broadside pattern multiplication faster than they contribute endfire gain (at ~.187 spacing when the primary endfire cell has .25 wl spacing).

If the array is made so small that there is little broadside contribution from array width, then the addition of the four will improve things. There isn't any broadside pattern to hurt. That isn't the same as a broad general statement that using more of the elements allows the array to be made smaller, unless we want to compromise pattern to have the same directivity.

I go through similar things with Yagi arrays. All of my Hygain 5 element Yagis have been changed to four elements, and my KLM six elements have become 5's. :) It isn't so much they work better, they just work different in a way that is a better compromise for pattern, bandwidth, complexity, and gain.

Everything is a compromise. If the target is maximum directivity and a clean pattern (more like a flashlight), the array has to be large. It can never be the same if small, or we all be running multi-element short boom antennas in close-spaced stacks.

I do agree, however, if space is so limited the array can't use broadside multiplication (which is the same as stacking gain in a Yagi array) then all active elements with more elements is better.

73 Tom

----- Original Message ----- From: "Lee K7TJR" <> To: "'Tom W8JI'" <>; "'Bob Tabke'" <>; <>
Sent: Monday, December 15, 2014 11:09 PM
Subject: Re: Topband: 8 circle: DXE vs Hi-Z

The primary difference between DXE and Hi-Z 8 circle arrays is the fact that Hi-Z uses ALL 8 verticals actively at the same time where DXE uses only 4 at
a direction.
Using all 8 verticals allows the use of a smaller diameter and a
performance edge on Directivity over the larger 4 active array.
All 8 element arrays do NOT work the same way.
  Lee  K7TJR

-----Original Message-----
From: Topband [] On Behalf Of Tom W8JI
Sent: Monday, December 15, 2014 7:24 PM
To: Bob Tabke;
Subject: Re: Topband: 8 circle: DXE vs Hi-Z

- DXE wants a 320' diameter and Hi-Z wants 200' for optimum performance.
It's hard to tell what DXE performance is because it does not disclose
RDF, beam width or F/B. And neither vendor supplies EZNEC files so I
can see the effect of varying the layout. So I'm not sure how to
decide what array size is best for me. It would be wonderful if
someone has a model for these two systems.


The ideal spacing of arrays like this is entirely dependent on the frequency
range and goal you have for pattern or directivity. It is NOT dependent on
the design or manufacturer, there are no magical space saving tricks.

The circle diameter determines both endfire and broadside spacing, and
spacing determines the beamwidth. Something in the 330-350 foot range across
the element pairs is near optimum for 160 directivity. You can use it down
to spacings where the element-to-element spacing is about 35-40 feet on 160, but it might as well be a four element vertical or some other array at that spacing. You can narrow the 160 pattern by going larger than 350 feet, but
the array can develop unwanted lobes. If element-to-element goes over 135
feet or so, you will start to have F/R issues.

This is the way every single eight element circle will work.

The primary difference between the DXE and Hi-Z is construction quality, and
that determines cost. The DXE unit is a metal case that serves as a
groundplane for the connectors, and a much better PC layout. How much that
translates into better performance depends on how "pure" the rest of the
installation is. If the installation is sloppy or compromised, that will set
the limit more than construction.

The DXE is a nearly direct copy of what I use here, which is a very clean
layout with PC mounted connectors and a super good groundplane between
connectors to prevent ground loops that affect performance and minimize
chances of lightning damage.

One reason I especially worry about connector grounding is my eight
verticals are spread in around a 350ft circle, and each has several 70 ft
buried radials. The large physical size of a system like this sets the
system up for large common mode currents in storms, it is actually a yearly event here to melt the shields off at least one cable with a nearby lighting hit (within a few thousand feet) because of ground loop currents, and yet I
almost never have box troubles.

I use a 20ft vertical with a small loading coil and series load resistor in
my elements, and a three wire hat.  Mine is single band 160 (although I'm
very slowly working on a 16-element circle for 160-80). People who operate
here just love the 8 circle.

I can send you an EZNEC file that would roughly approximate the array.

73 Tom

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