Physics
Coaxial Cable
A coaxial cable is a type of electrical cable consisting of a central conductor, an insulating layer, a metallic shield, and an outer insulating layer. It is commonly used for transmitting high-frequency electrical signals, such as in telecommunications and computer networks. The design of the coaxial cable helps to minimize signal interference and loss, making it an efficient choice for transmitting data over long distances.
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11 Key excerpts on "Coaxial Cable"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- White Word Publications(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter-1 Coaxial Cable RG-59 flexible Coaxial Cable composed of: A: outer plastic sheath B: woven copper shield C: inner dielectric insulator D: copper core Coaxial Cable , or coax , is an electrical cable with an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis. Coaxial Cable was invented by English engineer and mathematician Oliver Heaviside, who first patented the design in 1880. ____________________ WORLD TECHNOLOGIES ____________________ Coaxial Cable is used as a transmission line for radio frequency signals, in applications such as connecting radio transmitters and receivers with their antennas, computer network (Internet) connections, and distributing cable television signals. One advantage of coax over other types of radio transmission line is that in an ideal Coaxial Cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors. This allows Coaxial Cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines, and provides protection of the signal from external electromagnetic interference. Coaxial Cable differs from other shielded cable used for carrying lower frequency signals, such as audio signals, in that the dimensions of the cable are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a radio frequency transmission line. How it works Coaxial Cable cutaway Like any electrical power cord, Coaxial Cable conducts AC electric current between locations. Like these other cables, it has two conductors, the central wire and the tubular shield.
eBook - PDFPractical Industrial Data Communications
Best Practice Techniques
- Deon Reynders, Steve Mackay, Edwin Wright(Authors)
- 2004(Publication Date)
- Butterworth-Heinemann(Publisher)
The cable is remarkably stable in terms of its electrical properties at frequencies below 4 GHz, and this makes the cable popular for cable television transmissions as well as for creating local area networks (LANs). 2.3.1 Coaxial Cable construction A Coaxial Cable consists of the following layers (moving outward from the center) as shown in Figure 2.4. Carrier wire A conductor wire or signal wire is in the center. This wire is usually made of copper and may be solid or stranded. There are restrictions regarding the wire composition for certain network configurations. The diameter of the signal wire is one factor in determining the attenuation of the signal over distance. The number of strands in a multistrand conductor also affects the attenuation. Insulation An insulation layer consists of a dielectric around the carrier wire. This dielectric is usually made of some form of polyethylene or Teflon. Foil shield This thin foil shield around the dielectric usually consists of aluminum bonded to both sides of a tape. Not all Coaxial Cables have foil shielding. Some have two foil shield layers, interspersed with copper braid shield layers. 32 Practical Industrial Data Communications Figure 2.4 Cross section of Coaxial Cable Braid shield A braid (or mesh) conductor made of copper or aluminum that surrounds the insulation and foil shield. This conductor can serve as the ground for the carrier wire. Together with the insulation and any foil shield, the braid shield protects the carrier wire from electromagnetic interference (EMI) and radio frequency interference (RFI). The braid and foil shields provide good protection against electrostatic interference when earthed correctly, but little protection against electromagnetic interference. Sheath This is the outer cover that can be either plenum or non-plenum, depending on its composition. The signal and shield wires are concentric (coaxial) and hence the name.
eBook - PDFPractical Telecommunications and Wireless Communications
For Business and Industry
- Edwin Wright, Deon Reynders(Authors)
- 2004(Publication Date)
- Newnes(Publisher)
These have now almost all been replaced with fiber-optic systems. The only significant use of Coaxial Cables today is for cable television applications, particularly as hybrid fiber coax (HFC) systems discussed in Chapter 7. 3.4.1 Coaxial Cable components A Coaxial Cable consists of the following layers (moving outward from the center) as shown in Figure 3.12. 38 Practical Telecommunications and Wireless Communications Figure 3.12 Coaxial Cable components Carrier wire A carrier wire or signal wire is in the center of the cable. This wire is usually made of copper and is normally solid but may be stranded. There are restrictions regarding the wire composition for certain network configurations. The diameter of the signal wire is one factor in determining the attenuation of the signal over distance. The number of strands in a multi-strand conductor also affects the attenuation. Insulation An insulation layer consists of a dielectric around the carrier wire. The dielectric is often air, with a helical spacer made of polyethylene or Teflon. For short distance cables foamed or solid dielectric is used. Foil shield A thin foil shield around the dielectric. This shield usually consists of aluminum bonded to both sides of a mylar tape. Not all Coaxial Cables have foil shielding. Some have two foil shield layers, interspersed with copper braid shield layers. Braid shield A braid, or mesh, conductor, made of copper or aluminum, surrounds the insulation and foil shield. This conductor is normally connected to ground to create an electrostatic shield for the carrier wire. Together with any foil shield, the earthed braid protects the carrier wire from electromagnetic interference (EMI) and radio frequency interference (RFI). You should carefully note that the braid and foil shields provide good protection against electrostatic interference when earthed correctly, but little protection against magnetic interference.
eBook - ePubBroadband Cable Access Networks
The HFC Plant
- David Large, James Farmer(Authors)
- 2008(Publication Date)
- Morgan Kaufmann(Publisher)
2.2. Coaxial Cable
Coaxial Cable is not the only option for transmitting broadband RF signals. Indeed, many early systems were built using open, parallel-wire balanced transmission lines, and a few even used an ingenious single-wire cable known as G-line, which had only a center conductor and dielectric. Coaxial Cable, however, offers the advantages of a high degree of shielding, coupled with relatively low-cost and easy connectorization.2.2.1. Definition
Coaxial Cable is constructed with a center conductor surrounded by a dielectric of circular cross-section and by an outer conductor (shield), also of circular cross-section. Signals within the normal operating bandwidth of Coaxial Cable have a field configuration known as transverse electric and magnetic (TEM). In the TEM mode, the electric field lines go radially between the center and outer conductor and are of uniform strength around a cross section of the cable, whereas the magnetic field lines are circular and perpendicular to the length of the cable (see Figure 2.1 ). In a cable with a continuous, perfectly conducting shield, no electric or magnetic fields extend beyond the outer conductor, preventing both signal leakage and ingress.Figure 2.1. Coaxial Cable basics.
2.2.2. Characteristic Impedance
Coaxial Cables have a property known as surge impedance or, more commonly, characteristic impedance, which is related to the capacitance and inductance, per unit length, of the cable. The characteristic impedance is most easily thought of in terms of the effect on signals being transported: if a cable is connected to an ideal pure resistor whose value is equal to its characteristic impedance, a signal transmitted toward the resistor will be entirely absorbed by the resistor and converted to heat. In other words, no energy will be reflected back up the cable.
eBook - ePubThe Global Cable Industry
Materials, Markets, Products
- Günter Beyer(Author)
- 2021(Publication Date)
- Wiley-VCH(Publisher)
Coaxial theory actually dates back to the days of Maxwell in the nineteenth century and the exploration of electromagnetism. In the mid-1800s the earliest telegraph and first telephone cables spanning the Atlantic were actually a central conductor, with a gutta-percha (latex) insulator. Seawater was actually used as the outer conductor for this coaxial design. The bandwidth for these early cables was 1.0–1.5 Hz.In 1937, initial field tests were conducted utilizing Coaxial Cables for television transmission between New York and Philadelphia. The result was the first live broadcast of the 1940 Republican National Convention. World War II halted the work on TV broadcasting, but after the war TV broadcasting research promptly resumed, with Coaxial Cable making it possible. Applications during this time ranged from communications to control cables, radar, and a myriad of others.Oliver Heaviside. Source: Smithsonian Libraries, https://commons.wikimedia.org/wiki/File:Oheaviside.jpg .Figure 12.112.2 Design: Components and Principles
Transmission of direct current (DC ) requires two conductors to complete the circuit. One of the conductors is often referred to as the “go” wire, and the other as the “return” wire (Figure 12.2 ).With radio frequency (RF ) transmission, the Coaxial Cable becomes a transmission line where the “go” wire is the inner conductor, and the “return” wire is the outer conductor. These two conductors share the same longitudinal axis, hence the name Coaxial Cable. The outer conductor serves as an electrical shield for the cable and is typically covered by an outer jacket sheath.Coaxial Cable components.Figure 12.212.2.1 Components
The inner conductor is typically a copper or copper-clad material. Cost and weight may be deferred using cladded conductors, which take advantage of a concept known as the Skin Effect1
- Xingcun Colin Tong(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
Depending on their application requirements, interconnecting cables can be classified as Coaxial Cable, twisted pair, ribbon cable, or fiber optics (Croop, 1997; Mroczkowski, 1997). Coaxial Cable is suitable for high-speed, single-ended driven applications, such as microwave, radio frequency (RF) transmission, Internet, and other applications requiring high bandwidth. Coaxial Cable has zero loop area and shielding compo-nents, and good performance over controlled impedance ribbon, but it is usually bulky, difficult to terminate, and expensive. Twisted pair cable has a small loop area, and reduced crosstalk or electromag-netic induction between pairs or wires, as two insulated conductors are twisted around each other. Twisted pair cable is usually used for low-speed data transmis-sion, analog and digital applications, and differential drive. Shielded twisted pair cable has more reduced pair-to-pair crosstalk and additional protection against EMI, and it is mainly used for high-speed data transmission. 258 Advanced Materials and Design for Electromagnetic Interference Shielding Ribbon cable is better than buddle for shielding, has a low cost, and high longi-tudinal flexibility. It is easy to shield but hard to terminate with shield. Ribbon cable is mainly used for low-speed internal applications, such as printers, scanners, and other repeated flexing applications. Controlled impedance ribbon can be used for high-speed applications with high temperature and abrasion resistance. Fiber optics is one of the best and most promising cables for shielding, although it is relatively expensive. A fiber-optic system is similar to the copper wire system that fiber optics is replacing. The difference is that fiber optics use light pulses to transmit information down fiber lines instead electronic pulses. At one end of the fiber-optics system is a transmitter. This is the place of origin for information com-ing onto fiber-optic lines.
eBook - ePubCCTV
From Light to Pixels
- Vlado Damjanovski(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
The idea behind the coaxial concept is to have all the unwanted EMI induced in the shield only. When this is properly grounded, it will discharge the induced noise through the grounds at the camera and monitor ends. Electrically, the Coaxial Cable closes the circuit between the source and the receiver, where the coax core is the signal wire, while the shield is the grounding one. This is why it is called an unbalanced transmission.Most of the analog CCTV system would use Coaxial Cables for distances of up to a couple of hundred meters, before using an amplifier. Coaxial Cables are used today in the broadcast industry for digital serial signals (SDI) as well, although maximum distances are shorter for HD signals (1.5 Gb/s or 3 BGb/s).In the early days of networking, coax was used for the first 10Base2 Ethernet 10 Mb/s networks.Noise and electromagnetic interference
How well the coax shield protects the center core from noise and EMI depends on the percentage of the screening. Typically, numbers between 90 and 99% can be found in the cable manufacturer's specifications. Have in mind, however, even if the screening is 100%, that it is not possible to have 100% protection from external interference. The penetration of EMI inside the coax depends on the frequency.Theoretically, only frequencies above 50 kHz are successfully suppressed, and this is due mostly to the skin-effect attenuation. All frequencies below this will induce current in smaller or bigger form. The strength of this current depends on the strength of the magnetic field. Our major concern would be, obviously, the mains frequency (50 or 60 Hz) radiation, which is present around almost all man-made objects.This is why we could have problems running a Coaxial Cable parallel to the mains. The amount of induced electromagnetic voltage in the center core depends first on the amount of current flowing through the mains cable, which obviously depends on the current consumption on that line. Second, it depends on how far the coax is from the mains cable. And last, it depends on how long the cables run together. Sometimes 100 m might have no influence, but if strong current is flowing through the mains cable, even a 50 m run could have a major influence. When installing, try (whenever possible) not to have the power cables and the Coaxial Cables very close to each other; at least 30 cm (1 ft) would be sufficient to notably reduce the EMI.
eBook - PDFRadio and Line Transmission
The Commonwealth and International Library: Electrical Engineering Division, Volume 2
- Dermot Roddy, N. Hiller(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
Where large powers have to be carried, the coaxial system illustrated in Fig. 3.12(a) may be used at low and medium frequen-cies. Here the outer conductor consists of eight separate conductors connected in parallel and arranged as a cage around the inner coaxial conductor. The inner conductor itself may be a smaller cage of wires or it may be in the form of a tube as shown. At higher frequencies (e.g. above 30 MHz) a completely shielded coaxial system is usually necessary. Figure 3.12(b) shows one form of cable suitable for handling powers up to 30 kW. The two concentric tubes are made of copper, the outside diameter of the inner one being 0-875 in. (22 mm), and the inside diameter of the 62 R A D I O A N D LINE TRANSMISSION FIG. 3.12. (a) Coaxial feeder suitable for low/medium frequency, high-power applications, (b) Coaxial feeder suitable for high-frequency medium-power applications. (Reproduced by permission of H.M. Postmaster-General.) outer one being 3-25 in. (83 mm). With these dimensions the char-acteristic impedance is 75 Ω. Balanced feeders may also be used, and the main advantages of these compared with the coaxial feeder are : matching is generally easier; the open-wire type is simpler to construct and therefore is less costly; testing and maintenance on the open-wire type is easier. The main disadvantages are that the performance of the line may vary with weather conditions, and losses and interference (a) (b) TRANSMISSION LINES A N D CABLES 63 due to radiation can occur. Figure 3.13(a) illustrates a low-power, screened, twin feeder. For large powers (e.g. up to 30 kW), open-wire lines are used and are arranged in a manner similar to open telephone wires, but special precautions may have to be taken to maintain equal wire lengths, thus avoiding unbalance. Balanced feeders may also be constructed from four wires, as shown in Fig.
eBook - PDFRF and Microwave Circuit Design
Theory and Applications
- Charles E. Free, Colin S. Aitchison(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
1 1 RF Transmission Lines 1.1 Introduction Transmission lines, in the form of cable and circuit interconnects, are essential components in RF and microwave systems. Furthermore, many distributed planar components rely on transmission line principles for their operation. This chapter will introduce the concepts of RF transmission along guided structures, and provide the foundations for the development of distributed components in subsequent chapters. Four of the most common forms of RF and microwave transmission line are shown in Figure 1.1. (i) Coaxial Cable is an example of a shielded transmission line, in which the signal conductor is at the centre of a cylindrical conducting tube, with the intervening space filled with lossless dielectric. The dielectric is normally solid, although for higher-frequency applications it is often in the form of dielectric vanes so as to create a semi-air-spaced medium with lower transmission losses. A typical Coaxial Cable is flexible with an outer diameter around 5 mm, although much smaller diameters are available with 1 mm diameter cable being used for interconnections within millimetre-wave equipment. Also, for very high-frequency applications, the cable may have a rigid or semi-rigid construction. Further data on Coaxial Cables are provided in Appendix 1.A. (ii) Coplanar waveguide (CPW), in which all the conductors are on the same side of the substrate, is also shown in Figure 1.1. This type of structure is very convenient for the mounting of active components, and also for provid-ing isolation between signal tracks. Coplanar lines are widely used in compact integrated circuits for high-frequency applications. Further data on coplanar lines are given in Appendix 1.B. (iii) Waveguide , formed from hollow metal tubes of rectangular or circular cross-section, is a traditional form of transmis-sion line used for microwave frequencies above 1 GHz.
eBook - PDF- Architecture Technology Architecture Technology Corpor, Architecture Technology Corpor(Authors)
- 2017(Publication Date)
- Elsevier Science(Publisher)
All of these concerns must be addressed before installing a new system or upgrading an existing one. For example, when planning for the future, it is usually cost effective to use shielded twisted-pair cable to provide room for network growth. At an additional cost of only $650 for the average network, shielded twisted-pair provides the capacity for the transmission of higher network speeds. It reduces EMI egress and ingress, and gives increased data security. 5.1.1 Cable Properties The unshielded twisted-pair cable, commonly called telephone cable, contains two insulated wires twisted around each other. If that same cable had a metallic covering, such as an aluminum polyester tape, it would be called shielded twisted-pair. This is the lowest priced and most commonly used cable in newly installed industrial computer networks. Coaxial Cable is a two-conductor transmission line comprised of one conductor completely enclosed within another, which serves as its shield. While twisted-pair and Coaxial Cables are metallic cables, fiber optic cable is made of glass and uses light transmitted through optical fibers for communication or signaling. Because of different construction properties, each of the cable types just mentioned has various inherent characteristics and electrical parameters. Examples include impedance, attenuation, crosstalk, and bit-rate capacity for twisted-pair and Coaxial Cables, and fiber size and bandwidth for fiber optic cable. 61 Factory Communications 5.1.1.1 Impedance and Attenuation Impedance is a critical consideration when choosing coaxial or twisted-pair cables for a computer system. Computer systems require that all installed cable have the same impedance to avoid reflections within the cable that could cause errors in the transmitted data. If the insulation material and wire sizes are the same, cables with higher impedance generally have lower rates of attenuation.
eBook - PDF- Robert Shimonski(Author)
- 2005(Publication Date)
- Syngress(Publisher)
In the same way, some cables will allow a network to transfer millions of bits data, while others can send a thousand times this amount. As we’ll see later in this chapter, the features of a particular type of cable can vary greatly. 68 Chapter 2 • Network Media www.syngress.com Because different types of cabling are available to use, it follows that there are also different types of connectors that may be used.The connectors fit on the ends of the cabling, and are designed to hold the wires or fibers within the cabling together, allowing them to make a connection when the connector is plugged into or coupled with a network device. If you think of a cable used on your telephone, each end of the phone cable has a connector that bundles the wires in the cable together in a specific way, so they can make a connection when the cable is plugged into the corresponding telephone or wall jack.The connectors on a network cable are the same, providing an interface for a device to connect to a cable. Fundamentals of Cabling Cabling is the wire or fiber medium that is used to connect computers and other net-work devices of your network together, and used to carry the data that is transmitted between them. While we’ll discuss each of the types of cabling in greater detail later in this chapter, there are three types of physical media that can be used on a network: ■ Coaxial Cable ■ Twisted-pair cable ■ Fiber optic cable Coaxial Cable, also referred to as coax , is the same type of cabling you see in most cable television installations today.A single copper wire at the center of the cable core is used to carry the signals, and is surrounded by layers of insulation that protect the wire and its transmissions. On networks, there are higher grades and different types of coaxial that may be used: thin (10Base2) or thick (10Base5) are two examples. The thin and thick kinds of coaxial cabling refer to the thickness of the cable.
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