Coaxial Cable and Where It Still Lives

Coaxial cable, or coax, is an older copper cable type built very differently from twisted pair. It has a single solid copper core surrounded by layers, all sharing one central axis — which is where the name comes from. Although twisted pair replaced coax in most networks, coax is far from dead. It still carries internet and TV into millions of homes, so the exam expects you to recognize it.

Coax has four layers around a common center:

• Center conductor — a solid copper wire carrying the signal.
• Dielectric insulator — plastic separating core from shield.
• Metallic shield — foil or braid blocking interference.
• Outer jacket — protective plastic cover.

This shielded design makes coax very resistant to EMI, letting it run long distances with little signal loss.

The thick shield wrapped around the center conductor is coax's standout feature. It blocks external electromagnetic interference and keeps the signal contained inside. This is why coax was used for long bus-network backbones in the past and why it works well for cable TV and broadband, where signals travel from a provider over considerable distances into the home.

Two coax types appear on the exam. RG-6 is thicker, better shielded, and used for modern cable internet and TV and satellite, especially over longer runs. RG-59 is thinner with less shielding, common in older installations and short runs like analog video. When in doubt for broadband, RG-6 is the right choice today because of its better high-frequency performance.

Coax uses screw-on or push-on connectors rather than RJ45. The most common is the F-type connector, the threaded plug on the back of a cable modem or TV. Older and lab settings used the BNC (Bayonet Neill-Concelman) connector, a twist-lock type once found on legacy coax Ethernet. Recognizing F-type and BNC by name is enough for the exam.

The biggest modern use of coax is cable broadband. Internet providers send data over the same coax that carries cable TV, using a standard called DOCSIS (Data Over Cable Service Interface Specification). A cable modem connects to the coax with an F-type connector and converts the signal into Ethernet for your router. Millions of homes get internet exactly this way.

Cable providers often use a HFC (Hybrid Fiber-Coaxial) network. Fiber carries data at high speed from the provider to neighborhood nodes, then coax handles the final run into each home. This blends fiber's long-distance speed with coax's low cost for the last stretch. It is a practical example of mixing media, a theme you will see again with fiber.

Coax has downsides that pushed it out of office LANs. It is thicker and stiffer than twisted pair, harder to route and terminate, and older coax LANs used a shared-bus design where one fault could break the whole segment. Twisted pair with switches proved cheaper, faster, and easier to manage for local networks, so coax retreated to broadband and video roles.

Coax remains common in three places:

• Cable internet — the line from the wall to your modem.
• Cable and satellite TV — signal distribution in homes.
• Some security cameras — older CCTV video runs.

You are unlikely to wire a new office LAN with coax, but you will absolutely encounter it as the broadband drop into buildings.

One technical detail: coax cables have a rated impedance, measured in ohms, and you must match it to the equipment. Cable TV and internet coax like RG-6 and RG-59 is 75-ohm. Older Ethernet coax (like the long-gone "thinnet") used 50-ohm cable. Mixing impedances causes signal reflections and errors. For the exam, simply associate broadband and video coax with 75 ohms.

For the exam, remember coax as a shielded copper cable with a center conductor, used mainly for cable internet and TV. Match RG-6 to modern broadband and RG-59 to older short runs, the F-type connector to cable modems, and BNC to legacy coax. Know that DOCSIS is the cable-internet standard and that HFC networks pair fiber with coax for the last mile.

Test your coax knowledge.

You learned that coaxial cable has a center conductor, insulator, shield, and jacket, giving strong interference resistance. RG-6 serves modern cable internet and TV; RG-59 suits older short runs. The F-type connector attaches to cable modems, while BNC appears on legacy gear. Cable internet uses DOCSIS over coax, and providers run HFC networks pairing fiber with coax for the last mile. Coax lives on in broadband, TV, and some cameras, even though twisted pair won the office LAN.