Here is the take on configuration of the Quad from the Cubex Quad folks. From their website:
"The two most popular configurations are the Diamond, and Square. From a performance perspective there is no difference, in fact the element configuration may have many different shapes, Circular, Triangle (Delta Loop), or Rectangular. The key criteria is that the loop length must be nominally one wave length, and the elements have to be symmetrical about a line through the feed point and bisecting the structure. Polarity is determined by were the feed point is located; on the bottom it is Horizontal, and on the side (90deg away) it is Vertical.
At Cubex we use both configurations depending mostly on the size of the structure (band), and other physical or mechanical considerations. Usually our large HF arrays are configured in the Square or Box, and our smaller VHF (2m / 6m) and the EXPO series are Diamond configuration. The ARRL Antenna Book states that the Diamond design is a superior mechanical design because the sloping element wires will shed water, thus reducing potential ice loading. We at Cubex take issue with that premise, and in fact we think it can be shown that the "Square" is stronger and no more susceptible to ice loading then the "Diamond" configuration and more important, it will support ice loads better.
Let me briefly elaborate on our premise - First consider that the damaging stress for most spreader arms is not "compression" (the force down the axis of the arm) but the bending moment. I think it can be argued that when it is cold enough to freeze rain, an exposed element wire is colder and promotes freezing and therefore there is NO run-off regardless of the angle. Considering this worst case that all element wires, regardless of orientation, will collect equal amounts of ice load; the Square configuration with it two supporting arms will be stronger.
Looking at the two figures below, visualize that the element wires above the boom are ice coated. If we assume that the 45 deg. sloping lines of the DIAMOND collect less ice than horizontal lines, it follows that the two "vertical" parts of the Square configuration will collect even less ice. Assuming that the ice load factor for the Diamond sloping elements are each 0.5, (a total of 1). So in the diamond configuration this ice load of 1.0 (one) is supported by only one arm or a 1:1 support ratio.
In the Square case assume the horizontal wire element load is 1.0, and the two verticals are each 0.25 for a total of load of 1.5. Therefore with the Square we have an Ice Load of 1.5 but "TWO" arms resisting the fore and aft motion for a support factor of 2 to 1.5 or 33% stronger! This analysis can be refined, but I think it makes the point why we at Cubex think the Square or Box configuration is superior for large HF arrays. An added benefit is the turning radius is smaller!
. -We welcome alternative analyses- "
They have some great before and after pics at the site of Ice loaded Quads that would make you think the antenna couldn't possibly survive the ice load on them. The after pics indicate otherwise. I can only guess these were from ice storms that did not have a wind component in the equation.
Great antennas, maybe someday I'll have a place to put one up.
www.cubex.com/index.htm
73's
Wayne C.
