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Cable Assemblies: Ignore Them and Be Sorry

In the fast-paced world of active devices and the very tangible area of test equipment, the lowly cable and associated connectors sometimes seem to be nearly invisible, in both the prototyping and production cycles. That's not only unfair to their self-esteem (to use the trendy parlance), but unwise. Sure, we hear that “everything is going wireless,” but the reality is that hard-wired signal interconnects are an indispensable and irreplaceable part of nearly all systems.

It gets more challenging: as more design engineers work on projects that extend into the gigaHertz and higher range, they'll have to learn to give more consideration to the cable assembly as a critical and even dynamic part of the design. If you look at RF/microwave-centric publications and web sites, about one-third of the ads and content are devoted to the subject. It's a world where second- and third-order parameters such as phase matching between two nominally identical assemblies (such as used for phased-array radar) become critical; even the temperature coefficient of a cable's specifications can be a concern. The assemblies are carefully engineered, modeled, tested, and fabricated energy waveguides with precise dimensions, special internal and external insulating materials, and more.

Fortunately, cable assemblies are getting some attention from diverse perspectives, as shown by these unrelated features I have seen in the past few months:

We hear a lot about counterfeit components—mostly ICs and passives—but we don't see much about the situation with cabling. Yet, it seems to be a serious problem, especially as the cable may work to some extent if not full spec. According to Cabling & Installer, their 2011 article on the subject Counterfeit cable exposed was among their top 10 articles in 2014, three years after publication! (Also see Counterfeit cable is getting ugly.) The result is a cable assembly that doesn't fully meet the operating spec and may sort-of work but only support lower data rates, or a PoE (Power over Ethernet) installation unable to provide the specification's power.

It's not just electrical performance, either. On the safety side, a cable’s insulation in most installations must be fire-rated to not support combustion, yet these fakes fall far short— and it's an issue that you won't know about until a fire breaks out. Would you have even imagined presumed copper cable that was really brittle aluminum, but with a copper cladding? Think of the installation and performance surprises on that one!

To read the rest of this article, visit EBN sister site EETimes.

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