CUBEX QUADS- Welcome Cubex Quads

Design & Icing

Diamond or Square?

What about Ice?

Design Considerations of the Cubical Quad Antenna

The two most popular configurations are Diamond and Square.  From a performance perspective there is no difference, in fact the element configuration may have many different shapes such as 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 where the feed point is located.  On the bottom for horizontal or on the side for vertical.

At Cubex Quads we use both configurations, depending mostly on the desired band and other physical or mechanical considerations.  Our large HF arrays (Skymaster, Mk-series and Mantis) are configured in the square configuration, where our hub assemblies are fitted to a round-tube boom and the feedlines can serve as support for the driven elements, fed at the bottom/center of the square.  This also allows for improved structural strength for our large arrays where icing may be a concern (more on that later).   However, our smaller VHF/UHF models are best suited to the diamond configuration, where the feed point can be situated on a spreader arm for easier assembly, improved support (where vertical polarization may be desired) and also allows for simplified tuning where wire lengths are more sensitive to length.  Likewise, the Expo-series, which are built on square-tube booms are mechanically best suited to the diamond configuration.

Icing Concerns

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 take issue with that premise, in fact we think it can be shown that the square is stronger and no more susceptible to ice loading than the diamond configuration and more importantly, it will support ice loads better.

Allow me to 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. We 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 minimal run-off regardless of the angle. Considering this as the worst case, where all element wires, regardless of orientation, will collect equal amounts of ice load, the square configuration with its two supporting arms will be stronger.

Considering both a diamond and square shape, assume that the element wires above the boom are ice coated.  If we also assume that the 45-degree 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.  If the ice load factor of the two sloping elements is each 0.5 (a total of 1), this would suggest that the load is primarily supported by the upper arm… a 1:1 support ratio.

In the case of the square, 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 with TWO arms resisting the fore and aft motion for a support factor of 2:1.5, which is 33% stronger!  This analysis can be refined, and while we haven’t mentioned the spreaders themselves, the same logic can be applied to sloping vs. horizontal arm geometry, but I think it makes the point as to why we believe the square configuration is superior for large HF arrays.  As an added benefit, the turning radius is also smaller!

-We welcome alternative analyses-

Surviving the Ice