Topband: 8 circle: DXE vs Hi-Z
w8ji at w8ji.com
Mon Dec 15 22:23:55 EST 2014
> - 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.
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