If we check the history of electric cables, the real demand for wires and Cables to conduct electric power began in 1871, with the invention of the first dependable dynamo.
The telegraph and telephone swelled demand for efficient methods of transmitting electric current and signals over long distances. The insulation back in the days was paper coated. Just imagine Paper-coated pitch wrapped each individual wire, insulating it from the others. The whole batch was then wrapped in paper. Some even suggested laying these batches in tubes coated in resin and placing them underground to keep curious young boys away from them.
In the case of cables, factors like resistance, capacitance and impedance all play a role. There’s also a great many more electrical sources, magnetic sources and broadcast radio frequencies today than there were in the days of paper and pitch insulation. All of these factors can affect a cable’s transmission. As a result, shielding is another important variable in audio and video cabling. Let’s check out the basic terminology which is used when we consider the transfer of electric current.
Electrons, Voltage and Current
Electrons, and therefore electric charges, move through conductors. If they didn’t, the world today would be a very different place. A flow of electrons (a charge) flows from a voltage or signal source (like a battery) through two conductive surfaces (that is, materials that allow electrons to pass through them).
Hook a wire to two ends of a battery and you’ve got flow. This movement of electrons has many characteristics. The two of interest at the moment are voltage and current. Voltage is like the “pressure” created by the flow of electrons. Current is the rate of the resulting flow.
Resistance is the quality of a material that restricts the free flow of electrons. As a conductor resists the flow of current through it, a small percentage of the energy dissipates.
Metal wires are good conductors and resist little of the current that runs through them, though there is some loss. They also have a large surface to volume ratio. This is crucial because, oddly enough, electrons travel over the surface of the wire and not through the middle.
Capacitance is the tendency of a material to store energy and block constant or low-frequency currents. Capacitors filter and store energy, among other things. Different conductors have different resistive and/or capacitive properties. A shielded cable has similar properties to a capacitor, as both consists of two conductors separated by some type of insulator.
Capacitance is a factor in cable design because it reacts with the impedance in a length of wire to strip away high frequencies. In the video, that means a loss of detail; in audio, a loss of clarity. In cables, the lower the capacitance, the better.
Shielding
There’s a lot of electrical and magnetic interference in the air these days. Other power sources, appliances, close proximity to radio or TV stations-all these and more can create noise picked up by your cable unless properly shielded.
A shield is another conductive material, normally a metal foil or a wire mesh, that encircles and protects the integrity of your cable. It absorbs outside signals and/or reflects them back to the outside world. It also keeps your signal within your cable. The relationship between the conductor and shield within your cable can increase the Cable’s capacitance. Once again, careful design is everything.
Impedance
Audio and video signals are alternating current signals. They’re similar to waves, like sine waves. For a wave to pass cleanly across a cable from one component to another, the impedance-or signal opposition-must be equal all the way across. The cable must be rated to carry signal at a certain impedance.
If the impedances do not match between signal source, cable and receiving component, the waves get out of phase and collide with each other. This actually reflects some of the power of the signal back to the source, causing noise and signal loss.
The more reflection, the less clean your signal, ultimately leading to loss of picture or color data. The video signal is a high-frequency one, very susceptible to problems with impedance.
The Coaxial Cable
You’ve no doubt heard the term coaxial-coax for short-throw about. Fancy word, simple concept: coax simply refers to any cable with a central wire surrounded by an insulator, a shield and a plastic outer jacket. if you’ve seen almost any kind of AV cable other than cheap speaker wire, you’ve seen the coaxial cable.
In this article, we have checked the terminology related to cables and connectors. Do check out LAPP, one of the leading cable manufacturers in India, to purchase the best quality cables and connectors.
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