What Is a Coaxial Cable?

What Is a Coaxial Cable?

Cylindrical in shape, coaxial cables consist of four parts:

• External jacket

• Protective conducting shield

• Insulating dielectric material layer

• Internal metal conductor

“Coaxial” refers to the geometric axis the outer shield and inner conductor share. Unlike simple shielded cables transmitting low-frequency signals, coaxial cables offer superior transmission and reception capabilities, conducting alternating currents of radio frequency (RF). They’re a common choice for cable television, broadband Ethernet, and commercial radio transmissions.

How Do Coaxial Cables Work?

The central metal conductor transmits RF signals, with the surrounding layers facilitating. The dielectric insulator ensures that the spacing between the conductor and shield layer remains consistent for the full cable length while keeping their two signals from coming into contact and canceling out. The metal conducting shield safeguards signals against EMI and signal loss, creating a magnetic field with the conductor. Finally, the plastic cable jacket offers protection and insulation for the internal components.

While traditional shielded cables are used to transmit lower frequency signals, coaxial cables function as transmission lines, conducting alternating currents of radio frequency signals. With superior transmission and reception capabilities, coaxial cables are commonly used for broadband Ethernet, cable television, and commercial radio.

What Are The Different Types of Coaxial Cables?

Coaxial cables differ in design depending on their end use. Shorter cables often appear in household applications such as AV systems or personal Ethernet connections, while longer cables can connect entire radio and television networks or long-distance phones. Micro/mini cables are also frequently used in various consumer, military, aerospace, and medical devices.

Below are some of the most common coaxial cable types and the applications they support.

Hardline

Constructed using copper, silver, aluminum, or steel for the center conductor and one of these materials for a shield, these thick cables (≥ ½-inch diameter) are used for high-strength transmission in applications such as military signals or broadcasting radio between a ground-level transmitter and an antenna or aerial receiver. Hardline cables may contain a dielectric buffer such as polyethylene foam or pressurized nitrogen to prevent arcing and moisture contamination. Shield materials vary from piping to rigid or corrugated tubing.

Radiating

Also called “leaky cables,” radiating cables have a similar structure to hardline but with the addition of slots cut into the shield, tuned to specific wavelengths or radio frequencies. By allowing a pre-determined amount of “leakage” between the transmitter and the receiver, these cables can be implemented in locations where antennas are not feasible.

Twinaxial

Also known as “Twinax,” these cables share the same structure as coaxial cables but have two central conductors instead of one. They are used for high-speed, short-range signaling applications, such as network hardware with SFP+ interfaces.

Triaxial

Also known as “Triax,” these cables share the same structure as coaxial cables but have an added layer of insulation and a second conducting sheath. These cables are more expensive than standard coaxial cables but provide greater bandwidth and less interference for television production or applications exposed to interference-inducing electromagnetic forces.

Semi-Rigid

With a PTFE-supported dielectric and a shield made of a solid conductor instead of stranded wires, semi-rigid coaxial cables offer better dielectric properties for enhanced performance at high frequencies. Compared to rigid cables, however, semi-rigid lines are limited in size and frequency transmission.

Rigid Line

Rigid coaxial cables contain two copper tubes and a PTFE dielectric buffer supported at both ends of the cable as well as at various intervals throughout which prevents bends. Ranging from ⅞-inch to 8³/₁₆-inch diameters, rigid lines are much bigger than semi-rigid cables and have the power capacities to operate TV and FM frequencies with multi-channel transmission.

RG-6

Made with either a copper clad steel (CCS) or bare solid copper (BC) center, RG-6 cables are probably the most common coax cable, as they are used to relay cable television signals. Derived from the WWII military-specification “Radio Guide,” they are available in four different application-specific variations:

• Plain — For standard indoor/outdoor house wiring

• Flooded — Contains an additional water-blocking gel for underground conduits

• Messenger — Contains a steel wire to bear the tension of the aerial drop of a utility pole

• Plenum — Surrounded by a Teflon-based outer jacket to meet the fire codes of ventilation ducts

Coaxial Cable Connector Types

There are also an array of connector varieties available, with options including:

• Bayonet Neil-Concelman (BNC) connectors. Miniature to subminiature in size, these RF coaxial connectors allow you to quickly connect with and disconnect from television, radio, RF equipment, and testing instruments.

• Threaded Neil-Concelman (TNC) connectors. These miniature coaxial connectors operate at frequencies as high as 12 GHz. A weatherproof option, TNC connectors are applicable in creating RF/antenna and cellphone connections with minimized stability and leakage issues.

• Subminiature version B (SMB) connectors. Featuring an easy snap-on design on the coupling, SMB connectors are a tinier variety of SMA coaxial connectors. Ideal for semi-rigid cables with infrequent connections, they offer enhanced electrical performance, from DC to 4 GHz.

• 7/16 Deutsches Institut für Normung (DIN) connectors. These threaded RF coaxial connectors are compatible with cell network high-watt transmissions. 7/16 DIN connectors are also applicable for defense projects and antenna systems featuring several transmitters.

• QMA connectors. Offering quick-lock and -disconnect capabilities, QMA coaxial connectors are a type of SMA connector and share matching internal structuring.

• Micro coaxial (MCX) connectors. Compared to SMB varieties, MCX coaxial connectors have an OD of approximately one-third the size. Their operational frequency ranges from DC to 6 GHz, a good option for television tuner cards, wireless internet, digital cellular needs, GPS, and RF hardware.

• Radio Corporation of America (RCA) connectors. You’ll find these red, white, and yellow cords behind your television. Also called cinch connectors, RCA connectors are recognizable for their male connector end encompassed by a ring.

Key Factors to Consider When Choosing a Coaxial Cable

A coaxial cable’s radio guide (RG) number doesn’t always tell the whole story; there are a number of other factors to consider when selecting a cable for your unique application.

• Application — How will you be using your cable? Certain types are designated for specific applications, such as signal transmission for military operations, while others are designed for general use. Consider if your application will require short- or long-range transmission, as well as high or low frequencies.

• Impedance — Impedance refers to an electrical circuit’s resistance to alternating currents, expressed in ohms. Impedance should match throughout all components of a coaxial cable system to help prevent echoes, signal attenuation, and ghosting television images.

• Environment — Cables installed underground should pass through waterproof pipes to protect the jackets from liquid and vapor permeation. Users can also employ waterproof cords with self-amalgamating tape. To provide relief from sunlight and corrosive vapors, some manufacturers make use of hardened polyethylene cables, as well as tin and silver coatings.

• Working voltage and power rating — A coaxial cable’s voltage travels through the center wire or conductor. Each cable has a calculated maximum or “peak” voltage, which is then slightly reduced as a safety precaution.

• Signal loss at specific frequencies — Coaxial cable lines can be susceptible to signal loss at very high frequencies (VHF) and ultra-high (UHF) frequencies. Some manufacturers provide a foil or braided shield for VHF and UHF interference protection.

Common Applications — What Are Coaxial Cables Used For?

Coax cables have myriad applications across industries. Common coaxial cable uses include:

• Transmitting data while preventing attenuation loss

• Amplifying cellphone signal for enhanced cell reception indoors

• Connecting high-speed broadband internet between a cable line and a modem

• Connecting televisions, home video equipment, and radios to antennas, satellites, and related receivers

• Providing television or internet service to individual offices, apartments, or residences from a primary cable line