Coaxial Cable Layers, Builds, and Specs Explained

Coaxial cable is a cylindrical transmission line with a central conductor, a dielectric insulator, a metallic shield, and an outer jacket, and its performance is defined by impedance, attenuation, and shielding effectiveness. This article explains each layer, the common build types, and the key specifications that determine which cable you should use for a given application.

What Is Coaxial Cable?

Coaxial cable (coax) carries high-frequency electrical signals with low loss and high immunity to external interference. The name comes from the shared geometric axis of the inner conductor and the outer shield. It has been used since the mid-20th century for television distribution, radio transmission, and data networking. The design confines the electromagnetic field inside the cable, which prevents radiation and keeps outside noise from entering the signal path.

The Layers of a Coaxial Cable

A standard coax cable has four concentric layers, each with a specific job.

• Center conductor – carries the signal. It is usually solid copper or copper-clad steel (CCS) for cheaper cables, or copper-clad aluminum (CCA) for lightweight drops. Solid copper gives the lowest loss but costs more.
• Dielectric insulator – the non-conductive layer between the center conductor and the shield. It determines the cable’s impedance and affects signal speed and attenuation. Common materials are solid polyethylene (PE), foam PE, and air-spaced PE. Foam dielectric has lower loss than solid for the same diameter.
• Shield – the outer conductor that blocks interference and contains the signal. It can be a solid metal tube, a braided wire mesh, a foil wrap, or a combination. Braided shields are flexible; foil shields give 100% coverage but are less flexible. Double or quad shields add extra layers for high-interference environments.
• Outer jacket – the protective plastic sleeve, usually PVC or polyethylene. It provides mechanical strength, moisture resistance, and UV protection for outdoor use.

Some cables also include a messenger wire or a drain wire for grounding, and some have a rip cord to make stripping easier.

Common Coaxial Cable Builds

Coax is categorized by its impedance and its intended use. The two most common types are 50-ohm and 75-ohm.

• RG-6 – 75-ohm cable, the standard for modern TV and satellite signals. It has a thicker center conductor and better shielding than RG-59, allowing lower loss at higher frequencies. It is used for cable TV, satellite, and over-the-air antenna feeds.
• RG-59 – 75-ohm cable, thinner and more flexible than RG-6. It was common for analog CCTV and older TV installations. It has higher loss at high frequencies, so it is not recommended for long runs or high-bandwidth signals.
• RG-11 – 75-ohm cable with a larger diameter and lower loss, used for long outdoor runs (over 100 meters). It is stiffer and harder to terminate.
• RG-58 – 50-ohm cable, used for radio, Ethernet (10BASE2), and test equipment. It has a thin center conductor and a single braided shield.
• RG-213 / RG-8 – 50-ohm cables with thicker conductors and lower loss, used for amateur radio and other high-power RF applications. They are heavy and not very flexible.
• Hardline – 50 or 75-ohm cable with a solid aluminum outer conductor. It has extremely low loss and is used for base station antennas and cable TV trunk lines. It is rigid and requires special connectors.

Key Specifications: Impedance, Attenuation, and More

Several specifications define how a coax cable performs.

Impedance is the most important spec. It is the ratio of voltage to current at any point along the cable, and it is determined by the diameters of the conductor and the dielectric and the dielectric constant. Standard values are 50 ohms for radio and data, and 75 ohms for video and TV. Using a cable with the wrong impedance causes signal reflections, which reduce power transfer and create ghosting or data errors.

Attenuation is the loss of signal strength per unit length, usually expressed in decibels per 100 meters (dB/100m) at a given frequency. Higher frequencies attenuate more. For example, a typical RG-6 has about 5 dB/100m at 100 MHz and 11 dB/100m at 1 GHz. Lower loss means a longer usable run.

Velocity factor is the speed of the signal in the cable as a fraction of the speed of light. It depends on the dielectric material. Solid PE has a velocity factor of about 0.66, foam PE about 0.82. This matters for precise timing in radio systems.

Shielding effectiveness is the ability to block external interference. It is measured in dB, with higher numbers being better. A quad-shield cable can offer 90 dB or more of shielding at high frequencies, while a single braid might offer 60–70 dB.

Capacitance is the amount of charge stored per unit length, typically around 50–70 pF/m for 75-ohm cables. It affects the low-frequency response and is important for video signals.

How to Choose the Right Coaxial Cable

Choosing coax depends on the signal frequency, the length of the run, and the environment.

1. Determine the impedance you need – 75 ohms for TV/video, 50 ohms for radio/data.
2. Estimate the total cable length. For runs over 50 meters, choose a lower-loss cable like RG-11 or hardline.
3. Consider the frequency range. Satellite signals (up to 2.3 GHz) need RG-6 or better; old analog CCTV (below 10 MHz) can work with RG-59.
4. Assess the interference level. Near power lines, motors, or radio transmitters, use double or quad-shield cable.
5. Check the environmental rating – outdoor cable needs a UV-resistant jacket and may need to be buried in conduit.

Common Problems and Misconceptions

One common mistake is using RG-59 for satellite TV because it is cheaper and easier to bend. At 2 GHz, RG-59 loses more than twice as much signal as RG-6, so the picture may break up. Another mistake is mixing 50-ohm and 75-ohm cables in the same system, which causes reflections. Also, many people believe that more shielding always means better signal, but shielding only helps with interference – it does not reduce attenuation. In fact, a thicker shield can make the cable stiffer and harder to terminate.

Frequently Asked Questions

What is the difference between RG-6 and RG-59?

RG-6 has a thicker center conductor and lower loss at high frequencies, making it suitable for satellite and high-definition TV. RG-59 is thinner, cheaper, and more flexible, but has higher loss, so it is only good for short runs of low-frequency signals like analog CCTV.

Can I use 50-ohm cable for TV?

Technically you can, but it will cause a mismatch with the 75-ohm input of a TV tuner, leading to signal reflections and a degraded picture. It is best to use the correct impedance for the system.

How long can a coaxial cable run be?

It depends on the signal strength and cable loss. For a typical cable TV signal, RG-6 can run up to about 100 meters before the signal becomes too weak. For satellite, the limit is often around 30–50 meters. Using a lower-loss cable like RG-11 extends the range.

What does “quad shield� mean?

Quad shield means the cable has four layers of shielding – usually two foil layers and two braided layers. It provides excellent protection against interference, but it is stiffer and requires special connectors that can handle the thicker shield.

Is solid copper better than copper-clad steel?

For signal quality, yes. Solid copper has lower resistance, which means less attenuation. Copper-clad steel is cheaper and stronger, but it has higher loss, so it is only suitable for short runs or where cost is critical.

Can I bury coaxial cable directly in the ground?

Only if it is rated for direct burial, meaning it has a waterproof jacket and a gel-filled core to prevent moisture ingress. Standard PVC-jacketed cable will degrade quickly underground. Even direct-burial cable should be placed in conduit for added protection.

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