Coaxial cable transmits data as electromagnetic waves guided through the space between two concentric conductors: a central copper wire and a surrounding metal shield. An electrical signal applied to the center conductor creates electric and magnetic fields that travel along the cable at near the speed of light, carrying everything from internet traffic to television channels on different frequency bands. It’s a simple, durable design that has kept coaxial cable relevant for decades, even as fiber optics have gained ground.
The Four-Layer Structure
Every coaxial cable is built around the same basic architecture, from the inside out: a center conductor, a dielectric insulator, a metallic shield, and an outer jacket. Each layer has a specific job in getting a clean signal from point A to point B.
The center conductor is typically solid copper, stranded copper, or copper-plated steel wire. This is where the electrical signal actually flows. Surrounding it is a dielectric insulator, usually solid or foamed polyethylene, that maintains a precise spacing between the center conductor and the outer shield. That spacing matters because it determines the cable’s impedance, a property that must stay consistent along the entire length or the signal degrades.
The outer shield is one to four layers of woven metallic braid and metallic tape, most commonly braided copper. It serves double duty: it carries the return current for the signal while also blocking outside interference. Finally, a PVC or similar plastic jacket protects everything from physical damage and moisture.
How the Signal Actually Travels
When a transmitter pushes an alternating electrical signal onto the center conductor, it creates an electromagnetic field in the dielectric space between the center wire and the outer shield. The electric field radiates outward from the center conductor to the shield, while the magnetic field circles around the center conductor. These two fields travel together down the length of the cable as a guided wave.
This is different from a radio antenna, which broadcasts waves into open air in all directions. In a coaxial cable, the electromagnetic energy is confined to that narrow cylindrical gap between the two conductors. The signal doesn’t radiate outward, and outside signals don’t easily get in. The result is a private, efficient channel for carrying information.
Modern cable internet providers use frequencies from about 5 MHz up to 1.2 GHz or higher across this channel. Different frequency bands carry different data streams simultaneously, which is how a single coaxial cable can deliver internet, television, and phone service to your home at the same time.
Why the Shield Matters So Much
The outer conductor acts as a Faraday shield, a grounded conductive barrier that intercepts external electric and magnetic fields before they can reach the signal inside. When an outside electromagnetic wave hits the shield, it encounters a sharp impedance mismatch. The shield’s low impedance compared to the incoming wave causes most of the energy to be reflected or absorbed rather than passed through. Any displacement current from nearby interference gets routed directly to ground instead of contaminating the data signal.
This is why coaxial cable can run alongside metal gutters, electrical wiring, and appliances without the signal loss you’d see in unshielded wires. It’s also why the shield must be properly grounded. A floating, ungrounded shield can actually increase noise pickup rather than reduce it.
What Causes Signal Loss
No cable transmits a signal forever without losing strength. In coaxial cable, the main culprit is attenuation: the gradual weakening of the signal as it travels farther from the source. Several factors drive this.
The most significant is the skin effect. Alternating current doesn’t flow evenly through the entire cross-section of a conductor. Instead, it concentrates near the surface, and the higher the frequency, the thinner the layer of metal that actually carries current. At 60 Hz, current penetrates about 8.5 mm into copper, but at the hundreds-of-megahertz frequencies used for cable internet, the effective conducting layer is microscopically thin. This reduces the usable cross-section of the conductor and increases its resistance, converting more signal energy into heat.
The dielectric material also absorbs a small amount of energy, and this loss increases with frequency too. Together, these effects mean higher-frequency signals fade faster over distance, which is why cable companies place amplifiers at regular intervals along their networks.
How Far the Signal Reaches
A general rule of thumb puts coaxial cable’s usable range at about 500 meters (roughly 1,600 feet) before signal loss becomes a problem, but the actual distance depends heavily on the cable type and the frequencies involved. An RG6 cable, the most common type in residential installations, is typically reliable up to about 1,000 feet. An RG59, an older and thinner design, tops out around 750 feet. Thicker cables like the RG11, with its 14 AWG center conductor compared to RG6’s 18 AWG, can carry signals well over a kilometer thanks to lower attenuation.
For longer runs, cable providers install amplifiers or line extenders that boost the signal back to usable levels. In a neighborhood cable network, you’ll find these devices spaced throughout the distribution system between the headend facility and your home.
Common Cable Types Compared
All three widely used residential coaxial cables (RG59, RG6, and RG11) share a 75-ohm impedance and a copper-clad steel conductor, but they’re built for different situations.
- RG59 is the thinnest at 22 AWG. Its signal loss at high frequencies is too steep for most modern applications, though it still works fine for basic antenna connections and some analog CCTV setups.
- RG6 at 18 AWG is the standard for indoor use. It handles cable internet, satellite TV, digital antennas, and security cameras well. If you’re wiring anything inside a building, this is almost always the right choice.
- RG11 at 14 AWG is thicker and stiffer, designed for long outdoor runs and direct burial. Its low attenuation makes it the best option when cable needs to travel hundreds of meters, but it’s overkill and hard to work with for short indoor connections.
Turning Electromagnetic Waves Into Internet Data
The physical cable carries raw electromagnetic waves, but turning those waves into usable internet data requires a protocol. Cable internet providers use a standard called DOCSIS (Data Over Cable Service Interface Specification), which defines how digital data gets encoded onto the radio-frequency signals traveling through the coaxial cable.
Your cable modem receives the incoming RF signal, isolates the frequency bands assigned to data, and decodes the digital information embedded in those waves. It also transmits data back to the provider on a separate set of upstream frequencies. The latest version of this standard, DOCSIS 4.0, supports up to 10 Gbps downstream and 6 Gbps upstream, though real-world speeds depend on how the network is configured and how many users share the line.
This is a dramatic leap from early cable internet, which offered single-digit megabit speeds. The coaxial cable itself hasn’t fundamentally changed. What’s improved is the encoding technology: cramming more data into the same frequency spectrum by using more sophisticated modulation techniques, essentially packing more bits into each wave cycle.