The key to deciding what sort of RF cable assembly to use is one that revolves around mission criticality. As cable installation choices run up the ladder from flexible to semi-rigid to rigid, so too does the need for stable performance and reduced risk of RF or moronic human interference.
The basic purpose of any RF cable is to deliver an unadulterated signal from one electronic device to another. Since its invention by the English inventor and experimenter Oliver Heaviside in the surprisingly early year of 1880, coaxial, or RF, cable has been a stable platform for data transmission. The secret of RF lies in the concept of a carefully controlled distance between the inner core that transmits the data and the outer shield that surrounds it. These two conductive limits create an electromagnetic field in between them where the actual transmission of the desired signal takes place even as the outer shield layer blocks external sources of electromagnetic interference.
The basic flexible RF cable is used for such signal transmission needs as cable television operations and hard-wired computer network connections. Flexible RF is exactly that: flexible. Portable might be a better word, since the tail end of an RF cable is sufficiently mobile that it can be moved around as circumstances require without much difficulty.
The drawback of flexible RF is that it is designed for relatively weak signals that do not require a particularly high precision in the electromagnetic field that exists between the inner core and the outer shield. Slight variations in the distance between these two, such as might be caused by stapling the cable in place or severely bending it to go around a corner, do not matter in such low power applications.
Much stronger signals are carried in commercial, industrial and military RF systems than are found in ordinary consumer-grade RF cables. In these systems, signal interference is something to be avoided at all costs. A high-powered commercial radio transmitter, for example, cannot tolerate someone’s nearby cell phone conversation leaking onto the broadcast signal, nor can it be allowed to escape out into the open where it can, in turn, cause such strange phenomena as garage doors that apparently open and close by themselves at random intervals. A simple flexible RF cable is insufficient to guard against these dangers.
Both rigid and Semi-rigid RF cables are somewhat analogous to electrical conduit. Both are housed in solid tubes that are not intended to move around much once they are installed. The inner dimensions are more closely controlled than in flexible RF. This cuts down on signal leakage from the internal transmission as well as ghosting from the unwanted acquisition of signals from external sources.
In installations where signal quality is imperative and accidental severing or interruption is to be avoided at all costs, the rigid RF cable system is used, although it scarcely resembles a cable at all. Instead, rigid RF most closely resembles hard copper plumbing pipe, replete with standardized elbow assemblies for all bends in the system.
When looking at flexible vs. semi rigid vs. rigid RF cable assemblies, the issue is really one of collateral damage. If someone trips over a cable and sends their TV set crashing to the floor, that is not a good thing, but the impact is restricted to that particular household. As a result, flexible RF is a perfectly acceptable method of data transmission. In cases where the same clumsy oaf can put a radio station off the air or foolishly expose a secret military installation through signal leakage, there are important consequences that go beyond the impact on the one individual. In these cases, hardened RF cable assemblies are used to obviate the risks involved.
At MJS Designs All assemblies are 100% inspected and tested for continuity and special testing and test strategies are available.
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