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For better shield performance, some cables have a double-layer shield. [5] The shield might be just two braids, but it is more common now to have a thin foil shield covered by a wire braid. Some cables may invest in more than two shield layers, such as "quad-shield", which uses four alternating layers of foil and braid.
Twisted-pair cabling is often used in data networks for short and medium-length connections because of its relatively lower costs compared to optical fiber and coaxial cable. As UTP cable bandwidth has improved to match the baseband of television signals, UTP is now used in some video applications, primarily in security cameras . [ 6 ]
Cross-section through a coaxial cable showing shielding and other layers. One example is a shielded cable, which has electromagnetic shielding in the form of a wire mesh surrounding an inner core conductor. The shielding impedes the escape of any signal from the core conductor, and also prevents signals from being added to the core conductor.
A common type of 75 ohm coaxial cable is cable television (CATV) distribution coax, used to route cable television signals to and within homes. CATV distribution coax typically has a copper-clad steel (CCS) center conductor and a combination aluminum foil/aluminum braid shield, typically with low coverage (about 60%). 75 ohm cables are also used in professional video applications, carrying ...
The cable has an interrupted shield rather than a continuous shield, and the shield isn't grounded. Reading the patent (by Tesla) is interesting. It specifically argues that a coax cable is a bad thing due to cable losses, and it says that it is important to have a shield broken into segments shorter than the wavelength (which is incorrect).
For this reason, when attaching a twin-lead line to a coaxial cable connection, such as the 300 Ω twin-lead from a domestic television antenna to the television's 75 ohm coax antenna input, a balun with a 4:1 ratio is commonly used. Its purpose is double: First, it transforms twin-lead's 300 Ω impedance to match the 75 Ω coaxial cable ...