What Is Coaxial Cable? | The Backbone of Cable TV and Internet

That thick, round cable screwed into the back of your cable modem or TV antenna is coaxial cable—often shortened to “coax.” It works because of a simple but brilliant design: a copper conductor running dead center, surrounded by a foam insulator, then a metal shield, and finally a plastic outer jacket. The inner conductor and outer shield share the same axis—”coaxial”—which lets the cable carry radio-frequency signals over long distances without picking up electrical noise from nearby appliances, power lines, or Wi-Fi routers. If you’ve ever wondered why that one cable delivers both your internet and your TV channels, the answer lives inside its layers.

How Coaxial Cable Is Built

Coaxial cable is a precision assembly of four concentric layers, each with a specific job:

• Center conductor – Solid copper or copper-clad steel wire that carries the signal. In a standard RG6 cable, this is 18 AWG wire (about 0.040 inches in diameter).
• Dielectric insulator – Foamed polyethylene surrounding the conductor, keeping it perfectly centered so the electrical properties stay consistent along the cable’s length.
• Shielding – One to four layers of aluminum foil and braided wire that block electromagnetic and radio-frequency interference. Dual-shield has one foil layer plus one braid; quad-shield adds a second foil and braid for high-interference environments.
• Outer jacket – PVC or low-smoke material that protects the internal layers from moisture, sunlight, and physical damage.

The international standard IEC 61196-1 defines the generic requirements and test methods for these cables, ensuring consistency across manufacturers.

The Two Impedances That Matter: 50Ω vs. 75Ω

Coaxial cables come in two standard impedance values, and they are not interchangeable. Impedance—measured in ohms—determines how the cable handles signal power and reflection.

• 75-ohm cable (RG6, RG11, RG59) is the standard for cable television, video signals, and broadband internet. Your cable modem and TV antenna both use 75Ω coax.
• 50-ohm cable (RG58, RG8) is used for two-way radio equipment, data transmission, test gear, and ham radio antennas.

Plugging a 50Ω cable into a 75Ω system—or the reverse—causes signal reflection and loss. The mismatch degrades performance noticeably, especially at higher frequencies or longer cable runs.

Common Cable Types for Home and Professional Use

For most readers—whether you’re connecting a cable modem, setting up an over-the-air antenna, or running cable through a wall—RG6 is the straightforward choice. RG11 is thicker and stiffer but cuts signal loss on long runs. If you are deciding which cable fits your project, our tested roundup of the best coaxial cable options breaks down what to look for by use case.

Common Mistakes to Avoid

Coaxial cable installation seems simple, but a few errors can kill your signal or damage equipment:

• Impedance mismatch. Using a 50Ω cable in a 75Ω system—or vice versa—causes signal reflection and measurable power loss. Always match the cable’s impedance to your equipment’s specification.
• Connector type mismatch. Coax uses F-type connectors (common for TV and cable modems), BNC connectors (professional video and test equipment), or N-type connectors (higher-power radio). Using the wrong connector or a poorly crimped one introduces noise and signal drop.
• Bending the cable too sharply. Coax is bulkier than twisted-pair Ethernet cable and cannot bend at tight angles without damaging the internal dielectric geometry. If you kink it, the impedance changes at that point, and you get signal reflection.
• Skipping on shielding quality. In a room full of fluorescent lights, motors, or other electronics, single-shield coax may let interference in. Quad-shield is worth the extra cost in those environments.

For outdoor installations, moisture is the silent killer. Clean stripping of the polymer on the center conductor and proper sealing at connectors blocks moisture migration and keeps signal quality steady for years.

FAQs