Basics of Coaxial Connector Attachment
Coaxial assemblies are nearly ubiquitous for RF/microwave applications, with the exception of applications that require waveguide or planar transmission lines for efficiently conducting RF signals between components and devices. Hence, coaxial assemblies are found in use cases including within an assembly, bench-top instrument/device, indoor, outdoor, in aircraft, land-mobile vehicles, machinery, robotics, spacecraft, satellites, and more. Given the wide range of use cases, there are also a subsequently expansive variety of coaxial cable and connector technologies and features. Assembly of these coaxial technologies can be equally complex and require specialized tools.
However, there are several common types of coaxial cables and connectors that are assembled using a standard range of tools and methods. The origin of standardized coax is from military applications. The “Radio Guide” or RG number coaxial cables derived from World War II and were listed in the US MIL-HDBK-216 in 1962. Since then, RG number coaxial cable has become extremely common. This has given rise to common tools and practices for manufacturing RG coaxial assemblies, either within a facility, or manually during an installation or repair.
A typical RG coaxial cable consists of four layers, though there are many coaxial cables with additional layers. The four basic layers of a coaxial cable are the outer jacket (insulator), the metallic shield, the dielectric insulator, and center conductor. A coaxial connector is designed much the same way, with the exception of an outer jacket. In essence, the metallic shield, or outer conductor, of the coaxial cable must connect uniformly as possible with the outer shield of the coaxial connector, the dielectric insulator must meet with a coaxial connector in such a way to minimize impedance variations, and the center conductor must connect as uniformly as possible with the pin of the coaxial connector.
To attach these connectors, the coaxial cable’s outer jacket must first be removed, usually to a prescribed amount referenced from a precision cut coaxial cable end. It is important for the coaxial cable end to be cut cleanly in such a way that the coaxiality of the cable is not degraded and no metal fragments are impeded in the insulator. With the outer jacket removed, usually done with a prep tool that is precisely designed to strip the jacket without damaging the outer shielding, the shielding of foil, corrugated, or stranded conductor is mechanically manipulated to mate with the outer conductor fixture of the coaxial connector. Following this process, the dielectric insulator may be stripped back somewhat from the center conductor to enable soldering, crimping, or press fitting of the center conductor to the coaxial connectors center pin fixture. An additional ferrule is often included with the coaxial connector to strengthen the mechanical connector of the cable’s outer conductor and to ensure RF shielding. Once pressed, soldered, or otherwise fit together, additional heat shrink or tape is often used to ensure a stronger mechanical connection between the coaxial cables outer jacket and the coaxial connector. Adding heat shrink or tape at the mating interface between the cable and connector reduces strain on the joining of the conductors and dielectric, ensuring that the coaxial assembly will still perform as desired under some strain, load, or bending.
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Courtesy of Pasternack