Co-axial Cable
Follow the thick black cable that comes into a set-top box from the cable TV operator. Cut it and you will not find pairs of wires, but one copper wire in the middle, wrapped in layer after layer. Each layer has a job.
1What a co-axial cable is
“Co-axial” means sharing an axis: the core and the braided outer conductor are both centred on the same line, one inside the other.
2The four layers, from the inside out
- Copper core — carries the signal.
- Insulating material — keeps the core apart from the braid.
- Braided outer conductor — a mesh of copper that works as a shield, keeping outside noise away from the core.
- Plastic cover — protects everything inside.
Switch the noise on and watch the signal that arrives at the far end. Drag sideways to turn.
The braid's share is a teaching figure, not a measurement. A real co-axial cable is better shielded than an unshielded twisted pair.
The braid is the key to co-axial cable. NCERT calls its shielded design the key to its success: the core can carry data quickly without interference from its surroundings. That is why it is better shielded and has more bandwidth than twisted pair, and can carry signals of higher frequencies to a longer distance.
Think of a pipe inside a pipe
3Uses, advantages and disadvantages
Co-axial cable is used for cable television, to carry signals from CCTV cameras, and in some broadband internet connections. Older computer networks were built with it before twisted pair became common.
- Better shielded: much less affected by interference than twisted pair.
- Higher bandwidth than twisted pair.
- Carries signals over longer distances than twisted pair.
- More expensive than twisted pair.
- Thicker and stiffer, so harder to install and bend round corners.
- Lower bandwidth than fibre-optic cable.
4Check yourself
Which layer of a co-axial cable protects the core from outside electrical noise?
Compared with twisted pair, a co-axial cable is…