61 TRANSMISSION VIA CABLES What kind of cables do you have on your TV and computer? A grounding cable is connected to the ground (hence grounding ) because the mass of earth below our feet has a negative electrical charge. Positive electrical charges are naturally attracted to it, so any leakage of electric current is transferred to the ground for our safety. Fibre optic cables are non-conductive: they can t conduct electricity but can only transmit data. The maximum speed of fibre optic cable can reach 100Gbps (gigabits per second). This compares to the maximum speed of copper cables, which reaches as high as 300Mbps (megabits per second). Transmission lines consist of cables that connect different units of transmission. They are usually composed of copper wires, coaxial cables, or optical fibres. Types of cables There are different types of cables used in wired transmission . Twisted pair cables are used for transmitting data in small areas. They consist of two copper wires covered with insulating material which are twisted together to reduce electromagnetic radiation. They are further divided into: Shielded Twisted Pairs (STP), which are a special kind of copper telephone and local area network (LAN) wiring where wires are enclosed in a shield that provides greater protection from electromagnetic and radio frequency interference. With STP, a grounding cable is required; Unshielded Twisted Pairs (UTP), which are similar to STPs but do not have any metallic shielding around the wires and do not require any grounding cable. UTPs are easier to install, require less maintenance, and are cheaper. 142 ELECTRONICS AND ELECTROTECHNOLOGY Coaxial cables are made of an external PVC jacket, an internal metallic shield that contains a dielectric insulator, and a copper centre conductor. This type of cable is used in broadband Internet networking cables, cable television signals, and to connect radio transmitters and receivers to their antennas. Coaxial cables are more resistant than twisted pairs and more suitable for use over long distances. Fibre optic cables are used to transfer data signals in the form of light so they travel significantly faster and with less interference than those travelling in traditional electrical cables. They consist of several layers of protective plastic material that surround a glass core. The external protective layers make the fibre resistant and protect it from external damage or corrosion. It is suitable for areas with electrical interference and can be used to connect networks between buildings but also for very long distances. broadband: banda larga copper: rame core: nucleo leakage: perdita, fuoriuscita maintenance: manutenzione to shield: schermare