coaxial cable

A coaxial cable is a two-conductor transmission line where a single central conductor sits inside a tubular outer conductor, separated by a dielectric material. The outer conductor acts as a grounded shield that absorbs electromagnetic interference before it corrupts the signal traveling down the center wire. This geometry makes coaxial cable essential wherever high-frequency signals must travel without degradation, whether television video, RF measurements, or data at significant distances.

The construction matters. The inner conductor is typically solid copper or copper-clad steel, sized between 0.032 and 0.320 inches depending on impedance. The dielectric spacer, often polyethylene or foam polyethylene, maintains a precise distance between inner and outer conductors to set the cable's characteristic impedance, usually 50 ohms for RF work or 75 ohms for video. The outer conductor wraps tightly, either as a solid tube or as overlapping copper braid, and finally a tough outer jacket of PVC or polyethylene protects against mechanical damage and weather.

Why coaxial wins over other cables comes down to physics. A twisted pair will radiate and pick up stray fields; a shielded twisted pair helps but still leaks at high frequencies. Coaxial geometry creates a true field confinement: the electric field exists only in the dielectric between conductors, and the magnetic field sits only in that same region. Nothing leaks out if the outer shield remains unbroken and properly grounded at low-impedance points.

Where it fails

The main failure mode is shield degradation. Flexing, kinking, or repeated bending can crack the outer conductor or separate it from the jacket, breaking the electromagnetic seal. Water ingress into a compromised shield causes corrosion of the braid and rising attenuation. At connectors, poor termination leaves air gaps between the center pin and outer connector body, causing reflections and signal loss. Velocity of propagation in coaxial cable runs 0.66 to 0.80 times the speed of light, so phase shift accumulates over long runs; this matters in phased antenna arrays and precision timing applications.

Coaxial cable sits at a cost and complexity midpoint. It costs far more than unshielded twisted pair but delivers genuine immunity to industrial electrical noise. Fiber optic cable outperforms it at very high frequencies and over long distances but requires active termination and is fragile. For frequencies from DC to roughly 3 GHz, for runs of tens to hundreds of meters, and where connector rework is expected in the field, coaxial cable remains the default choice in radio frequency systems, test equipment, and broadcast infrastructure.