December 2005 - page 2
SIGNAL CABLES
 Ribbon Cable (lamp cord) is the simplest of all cable designs, featuring small-gauge (16-22) jacketed copper wire. This can be stranded or solid core, but utilizes no shield. Multiple conductors are laid out so that a ribbon effect is created, usually with some type of rainbow color scheme when used inside components. This type of wire experiences heavy use in computers and digital products like CD and DVD players, connecting one circuit board to another, neatly and speeding up assembly and repair. The lack of a shield limits the usable length of a ribbon cable to only a few feet due to power line and electromagnetic noise (EMI, RFI) leaking into the signal. However, in short lengths with low voltage signals, it is the wire of choice throughout the world of telecommunications today. It also makes up the bulk of the world’s speaker wire.
Twisted Pair is simply two wires that are intertwined uniformly over their entire length, usually inside a jacket. Twisting the wires rejects some EMI and RFI. Adding a shield (also intertwined), connected at only one end to prevent a ground loop from forming, will reject all but the strongest noise fields. This allows a twisted pair to be used for several hundred feet while one employing a shield can be used for several thousand feet without significant loss of signal.
Shielded Cable is a simple, insulated cable that features a braided, solid or taped shield made out of copper (or other metal), which completely encloses the conductors preventing undesired inductive currents from leaking in or out. The signal is therefore transmitted with significantly lower noise and distortion, and lengths can be quite long (over 10,000 feet) before significant noise creeps in.
Coaxial Cable, first patented in Germany by Ernst Werner von Siemens in 1884, consists of a round solid core conductor surrounded by a porous insulating spacer (usually foam), further surrounded by a cylindrically wound insulating shield (usually aluminum tape and four solid core 22-gauge drain wires in the case of RG-6), and finally a plastic jacket. Although originally used for telephone, radio and then analog television, this unbalanced cable has 75-ohm impedance due to its construction and geometry. It is therefore also ideal for use in digital audio, high-frequency broadband Internet, satellite and cable, as well as for broadcast video applications.
Fiber Optic cables are made out of a single strand of either glass or plastic that has a finely polished exterior. Light applied at one end naturally follows the direction of the strand to appear at nearly full strength at the other end. It is therefore not subject to EMI/RFI interference and is incapable of creating a ground loop. Low-resolution Toslink is adequate to carry compressed Dolby Digital and DTS soundtracks, while Hi-band ST format Digital Audio can carry high-resolution DSD and SACD, as well as HDTV video when used in groups of four cables.
Next topic, Connectors (Jacks)
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