coaxial cables

Coaxial means that two things share a single axis. The coaxial cable consists of three main parts: the inner conductor, the outer conductor, and the surrounding insulation. The inner conductor is usually a single wire that transmits the signals sent along the coaxial cable. The outer conductor is made of a different type of material and surrounds the inner conductor. Often, it is composed of foil or braided, copper wires. The surrounding insulation is the flexible material that is visible on the outside of the coaxial cable. If this surrounding insulation is thin enough, you can sometimes see the braiding of the outer conductor protruding in the well worn areas. How Coaxial Cable Works The way the coaxial cable works is simple. The signal that needs to be transmitted is sent along the inner conductor. The signal does not move in a straight line because the bends in the coaxial cable prevent this from happening. This is where the outer conductor comes into play. The outer conductor is composed of materials that work to reflex the signal off of the contact surface between it and the inner conductor. In this way, the signal is continually reflecting off of the outer conductor as it travels to its destination. Think of it like a racquetball bouncing off of the walls of a tube. And just like the racquetball, the signal loses energy as it travels the length of the coaxial cable. This loss of energy comes in the form of signal loss into the outer conductor. With each reflection off of the outer conductor, small amounts of signal are transmitted into it. This signal loss makes coaxial cable less than ideal for many applications, such as transmitting signals from your DVD player your television. Two types of coaxial cables RF and Digital There are two main signals used for transmission over coaxial cable, radio frequency (RF) and digital. The RF coaxial cable is the type you are probably most familiar with; it is used for transmitting signals for cable television, television antennas, VCRs, etc. RF coaxial cable sends both video and audio all along the single wire of the inner conductor. The RF coaxial cable itself comes in two flavors, RG-59 and RG-6. RG-59 is the type used most often for the applications that were previously mentioned. Occasionally, when you buy a VCR it will include an RF coaxial cable so that you can use it right out of the box. More often than not, this is an RG-59 cable. RG-6 is a higher quality RF coaxial cable which employs better shielding to reduce signal loss. Digital coaxial cable employs an RCA connector rather than the screw type used for RF coaxial cable. This type of coaxial cable is designed specifically for transmitting digital audio signals and nothing else. Since it is designed to send digital information, the need to convert digital signals into another medium is by-passed. This results in the elimination of audio artifacts that can result from such signal conversion.

In broadcasting and other forms of radio communication, hard line (also known as hard pipe) is a very heavy-duty coaxial cable, where the outside shielding is a rigid or semi-rigid pipe, rather than flexible and braided wire. Hard line is very thick, typically at least a half inch or 13 mm and up to several times that, and has low loss even at high power. It is almost always used in the connection between a transmitter on the ground and the antenna or aerial on the tower. Hard lines are often made to be pressurised with nitrogen or desiccated air, which provide an excellent dielectric even at the high temperatures generated by thousands of watts of RF power, especially during intense summer heat and sunshine. Physical separation between the inner conductor and outer shielding is maintained by spacers, usually made out of tough solid plastics like nylon. RG/6 is available in three different types designed for various applications. “Plain” or “house” wire is designed for indoor or external house wiring. “Flooded” cable is infused with heavy waterproofing for use in underground conduit. “Messenger” contains some waterproofing but is distinguished by the addition of a steel messenger wire along its length to carry the tension involved in an aerial drop from a utility pole. Triaxial cable or triax is coaxial cable with a third layer of shielding, insulation and sheathing. The outer shield, which is earthed (grounded), protects the inner shield from electromagnetic interference from outside sources. Twin-axial cable or twinax is a balanced, twisted pair within a cylindrical shield. It allows a nearly perfect differential signal which is both shielded and balanced to pass through. Multi-conductor coaxial cable is also sometimes used. Biaxial cable or biax is a figure-8 configuration of two 50 Ω coaxial cables, used in some proprietary computer networks. Semi-rigid cable is a coaxial form using a solid copper outer sheath. This type of coax offers superior screening compared to cables with a braided outer conductor, especially at higher frequencies. The major disadvantage is that the cable, as its name implies, is not very flexible, and is not intended to be flexed after initial forming. Applications :::::Short coaxial cables are commonly used to connect home video equipment, in ham radio setups, and in measurement electronics. They used to be common for implementing computer networks, in particular Ethernet, but twisted pair cables have replaced them in most applications except in the growing consumer cable modem market for broadband Internet access. Long distance coaxial cable is used to connect radio networks and television networks, though this has largely been superseded by other more high-tech methods (fibre optics, T1/E1, satellite). It still carries cable television signals to the majority of television receivers, and this purpose consumes the majority of coaxial cable production. Micro coaxial cables are used in a range of consumer devices, military equipment, and also in ultra-sound scanning equipment. The most common impedances that are widely used are 50 or 52 ohms, and 75 ohms, although other impedances are available for specific applications. The 50 / 52 ohm cables are widely used for industrial and commercial two-way radio frequency applications (including radio, and telecommunications), although 75 ohms is commonly used for broadcast television and radio.


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