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Cables and Cabling Infrastructure Part 1 – Basic Cable Construction ©PRGodin @ gmail.com Updated Dec 2013 This Presentation • This is a large presentation as it contains all the materials for basic copper cable including: ▫ ▫ ▫ ▫ ▫ Terminology Conductor styles Basic cable structures Jacketing Performance characteristics including resistance, capacitance, noise, throughput ▫ Grounding, twist characteristics 2 Cable? but wireless is the Future! • Those wireless access points need to be interconnected • Hard connections are more robust, more reliable, offer more control and are more secure • Wired has much higher data throughput, less latency • Wired is unaffected by weather, line-of-sight, interference, etc • Backbone connections need high performance only achieved with a wired network • CATV, ISP and Satellite communications need cables for distance. • Limited wireless infrastructure • Wired is less costly and easier to maintain in the long term • Power can be delivered via wired There will be fewer installations of wired ports at the user end but the infrastructure will, in the foreseeable future, always be wired. There are far too many advantages with wired networks. 3 Cable • Cable is a package of conductors or strands bound together. • Communication cable construction, compounds and structure affects its performance, application, installation and durability. 4 Conductors • There are many ways a copper conductor can be structured. • The two primary methods are: ▫ Solid ▫ Stranded • There are other arrangements of conductors for specific applications. 5 Solid Conductors • Solid: Single strand of copper ▫ Lowest cost ▫ Very poor flexibility – only used in fixed installations Image: china-cablewire.com 6 Solid Conductors • Bare Copper (BC): only copper ▫ Least expensive ▫ Susceptible to oxidization if exposed Un-oxidized copper wire (left) and oxidized copper wire (right). Oxides have high electrical resistance Image: wikipedia • Tinned Copper (TC): copper conductor with a coating of lead/tin, or silver ▫ Protects the conductors from oxidization ▫ Easier to solder ▫ More expensive 7 Stranded Conductors • Stranded: Multiple strands of copper twisted as a single conductor ▫ Flexible but more expensive • More individual strands increase flexibility and cost. Stranded Wire with High Strand Count Image: Wiki CC 8 Stranded Conductors • Stranded Bare Copper (SBC): strands of copper only ▫ Susceptible to oxidization if exposed • Stranded Tinned Copper (STC): each strand is coated with solder (Lead/Tin) ▫ Protects the conductors from oxidization ▫ Easier to solder ▫ More expensive image: forums.nasioc.com (user submission) 9 • Copper Clad ▫ A different metal (typically steel) is clad (covered) with copper. ▫ Used in high frequency applications where tensile strength is also desired. ▫ Many Coax cables have a copper covered steel conductor. Coax with Rigid Copper Shield and Copper Coated Steel Conductor Image: PRGodin Other Conductor Types 10 Other Conductor Types Image: PRGodin • Tubular (hollow tube) ▫ Specialized Applications ▫ Used in high frequency applications (due to Skin Effect) ▫ Large diameter cables ▫ Difficult to physically handle ▫ Very expensive Coax with Tubular Conductor 11 Other Conductor Types Image: www.maeden.com.tw • Tinsel & Polyester ▫ Tinsel or polyester weave for high flexibility devices such as headphones, earphones and microphones. ▫ Difficult to terminate and solder. Polyester Conductors 12 Other Conductor Types Image: internet (multiple sources) • Braid or Woven Wire ▫ Braid used for cable shielding ▫ Used for grounding applications Woven or braided Wire 13 Other Conductor Types Image: www.electrical-res.com • Aluminum and other elements ▫ Conductors may use elements other than copper: Aluminum Lighter and cheaper Typically larger gauge due to resistance Used for electrical applications Not as tolerant to flexing Cannot be mixed with copper Cannot be used for building wiring Aluminum Wire Gold & Platinum (solid or plated) Used in semiconductor applications Other 14 Why Copper? • Relatively abundant • Good corrosion resistance • Very malleable (ability to bend and reshape) • Relatively strong • Very ductile (capability to be made small) • Excellent conductivity for electricity and heat Image: www.ccbda.org 15 Conductor Size Wire sizing tool Image: Wiki CC 16 Conductor Size • Conductor diameter (size) is measured in American Wire Gauge (AWG), or just Gauge (sometimes spelled Gage) • Conductor size reduces with an increase in the gauge number. ▫ a 24 AWG conductor is much smaller than a 12 AWG conductor. • Typical sizes ▫ Data communications: 20 to 28 AWG ▫ Electrical 18, 16, 14 and 12 AWG (Residential and automotive) ▫ Much larger for industrial applications. 17 Conductor Size - Units • AWG is considered an “imperial” unit • Conductor sizes may be referred to by a metric value that represents cross-sectional area in square millimetres (mm2) • A 20 AWG wire is 1029 circular mils. This is between 0.6 mm2 and 0.5 mm2 in metric format. • Conversion tables are available on line. 18 Gauge Tools 19 Conductor Size - Stranded • Stranded conductors are referred to by both the overall AWG of the bundle, and the number and gauge of the individual conductors. ▫ Example: a “7x32” stranded conductor is made up of 7 strands of 32 gauge wire twisted together to make up a 24 AWG sized conductor 24 AWG Cross-section of a “7x32” conductor • More small-gauge strands makes the conductor more flexible but also makes it more expensive. 20 Jacketing Compounds Jacket Extrusion Unit (Training Model) Image: Wiki CC 21 Jacketing Compounds • The more popular cable jacket compounds used today are: ▫ PVC (polyvinyl chloride): A versatile and inexpensive compound, used for many indoor cables. ▫ PE (Polyethylene): Excellent electrical and environmental properties. Used for outside jacketing and as a dielectric for coax. Teflon: Excellent electrical and temperature properties. Nonflammable. Used in extreme temperature environments or Figure 4-33: Image of a tied-lace Teflonwhere fire immunity is desired jacketed cable bundle on NASA’s Curiosity such as alarm cable. Expensive. Rover in 2012 (with specks of Martian dust in the background). Image: NASA 22 Jacketing Compound – Outside • Direct Burial and “outside plant” applications ▫ Low density polyethylene often used. ▫ Water Repellent: gel or gas filled, expanding gel tape. ▫ Often require ducting or armor for mechanical strength and rodent resistance. ▫ Must be terminated within a few meters of building entrance due to fire regulations, lightning protection and ease of handling. 23 Jacketing Compound – Outside • Aerial Applications ▫ Air-filled or expanding gel tape for reduced weight. ▫ Requires a messenger cable for support. Can be lashed to a separate messenger or manufactured in a “figure-8” configuration. ▫ High UV and temperature resistance 24 Jacketing Compounds • There are many other compounds such as rubber, silicone and a variety of vinyls & plastics used in the industry for indoor and outdoor applications. • Each have a variety of physical and electrical properties that make them the best choice in certain environments. • Refer to vendor catalogs or web sites for more information. 25 Making Jacketed Wire • A large copper rod is warmed (not melted) • The copper rod is forced through a succession of dies ▫ Dies are made of very hard material ▫ Each die reduces the copper’s diameter by ~30% ▫ Small wire gauges need to pass 30 to 40 dies • Jacketing is then applied using an extrusion process Plastic (Pressure) Insulated Wire Wire Water (cooling) Image: PRGodin 26 Building Air • Cables are often run in the same space as the building air flow. • The area above a suspended ceiling is usually the return air from the living space and will be recirculated. This is known as an air plenum. • Columns of space between floors, such as an elevator shaft, are known as risers. 27 Cable Flammability • Cable jacketing compounds can be a serious problem should there be a fire. ▫ Burning cable jacketing produces highly toxic smoke and gases. PVC releases hydrogen chloride gas (hydrochloric acid) and other dangerous compounds when it burns, including large quantities of carbon monoxide. ▫ Cables run throughout a building often through open tray in air plenums. Cables and trays must have some resistance to spreading fire. • All cables must meet fire codes and must be installed within fire regulations. 28 Jacketing Compounds • Environmental issues, installation location and fire regulations dictate the jacketing required. • In most indoor office locations, fire rating are the main criteria: ▫ FT-1 rating for workstation cords ▫ FT-4/CMR/OFNR rating for most fixed applications in most provinces ▫ FT-6/CMP/OFNP rating for installations in BC, ON, PQ (check provincial code before installing). 29 Flammability (CSA) • FT-1: Cable self-extinguishes after 60 seconds. • FT-4: Chars for less than 1.5 meters. • FT-6: Chars for less than 1.5 meters and produces much less smoke. Will not sustain a flame. • For more information see the National Electrical Code (NEC), the Canadian Electrical Code (CEC) or the International Electrotechnical Commission (IEC). 30 Flammability Ratings • The CSA (Canadian) and UL (American) communications cabling standards were harmonized as a bi-national standard. The identification of cable flammability for the US and Canada is as follows: ▫ MPP or CPP or CMP: Multi-Purpose Plenum or Communication Plenum. FT-6 rated. ▫ MPR or CPR or CMR: Multi-Purpose Riser or Communication Riser, for riser cable identification. FT-4 rated. ▫ MPG or CPG or CMG : Multi-Purpose General use or Communication General use. FT-4 rated. ▫ CM, CMH or CMH: FT-1 rated. 31 Resources • Belden Inc, a cable manufacturer, has excellent information on jacketing compounds. ▫ www.belden.com 32 Cable Markings Optical Cable markings for fire ratings. The markings include terms such as OFNR & Riser, OFN & FT-4, and OFNP & Plenum. Image: PRGodin 33 Cable Markings • Communication cable jackets contain print that typically includes many of these elements: ▫ Manufacturer ▫ Model Number ▫ Description (short form) #pairs or conductors Conductor characteristics Type of cable (may be an industry number) ▫ UL and/or CSA and/or ETL indication (may include registration number) ▫ Manufacturing date ▫ Meter length marking ▫ Code compliance 34 Cable Markings • Example of a cable marking: Mohawk/CDT 25 PR 24 AWG (UL) C(UL) CMR or MPR---- ETL Verified to TIA/EIA 568- A Cat 5---Patent Pending----M56753 B115-6 022922 ft 35 Elements of a Cable 36 Image: http://www.rictec.com.sg Image: PRGodin Definitions: Shielding • Shielding: Reduces electrical noise. ▫ Braided wires: Coverage expressed in % (can never achieve 100% coverage). Helps to maintain cable shape. Cable foil shield (STP cable) image: www.customdesignedcable.co.uk ▫ Foil: Often polyester covered with a conductor. Can achieve 100% coverage. Cable Braid 37 Definitions: Shielding • Rigid Tape: A thick metallic tape used for electrical and mechanical reasons. • Armor: Mechanical protection in the form of interlocked rigid steel or aluminum. Image: PRGodin •Drain Wire: A conductor that electrically connects to the shield Cable interlocking armour 38 Definitions: Structural • Filler: Inert extra materials added to help the cable maintain the proper shape. • Strength member: An element mainly used to maintain cable rigidity. • Aramid Yarn or Kevlar®: Used for strength (longitudinal or “pull”). Dupont Kevlar®. 39 Definitions: Structural • Gel Tape: A tissue-like material that expands into a gel-like substance when exposed to water. Image: PRGodin • Rip Cord or string: A string placed just inside a cable jacket, used to cut the jacket material away. Usually make of Dupont Kevlar® •Twinned or Siamese: Two cables joined as one at the jacket. Twinned Cat 5 UTP 40 Cable Images 41 Cable – Twisted Pair Unshielded Twisted Pair (UTP) Screened Twisted Pair (ScTP) Image: Wiki CC 42 Cable – Twisted Pair Jacket Filler Foil Shield Rip Cord (not shown) Insulated Twisted Pair Conductors Unshielded Twisted Pair (UTP) Drain Wire Screened Twisted Pair (ScTP) Image: Wiki CC 43 Cable – Shielded Twisted Pair (STP) Image: PRGodin 44 Cable – Shielded Twisted Pair (STP) Foil Shield (Individually Shielded Pair) Conductor Pairs Braided Shield Jacket Image: PRGodin 45 General Multiconductor Image: Wiki CC, PRGodin 46 Shielded Multi-conductor Overall Foil Shield Drain Wire Braided Shield Images: Wiki CC, PRGodin 47 Coax Cable Images: Wiki CC, PRGodin 48 Coax Cable Jacket Braided Shield Foil Shield Dielectric Copper coated steel conductor Images: Wiki CC, PRGodin 49 Fiber Optic -Indoor Distribution Primary use: interconnect panels and rooms within a building. Higher density of fibers for size, some strain relief. Image: PRGodin 50 Fiber Optic -Indoor Distribution Aramid Yarn (Kevlar) Buffered fiber strands Rip Cord Strength Member Image: PRGodin 51 Fiber Optic -Indoor Distribution Images: PRGodin 52 Fiber Optic – Indoor Breakout Primary use: Interconnect panels, outlets, rooms within a building. Used where good protection and connectorization is needed as there is a strain relief and jacket for each strand. Images: PRGodin 53 Fiber Optic – Indoor Breakout Strength Member Rip Cord Fiber Strand Overall Jacket Aramid Yarn Image: PRGodin Buffered Fiber Strand 54 Outside Plant Fiber Cable Images: PRGodin 55 Discussion points for Part 1 • What is the difference between a fiber optic breakout cable and a fiber optic distribution cable? • What fire rating is required for commercial installations in Alberta? Is a certificate acceptable in the absence of a cable marking? • In what instance would a solid conductor be inappropriate? • Which is bigger: a “00” AWG or a “20” AWG conductor? • Why are copper conductors sometimes “tinned”? • What is a “7x32” conductor? 56 Cables and Cabling Infrastructure Part 2 – Cable Selection and Color Code ©PRGodin @ gmail.com Updated Dec 2013 57 Selecting Cable 58 Selecting Cable • The effectiveness of a communications infrastructure is dependent on the cabling. • It is important to consider several factors when selecting telecommunications system cable. The five basic cable characteristics are: 1. 2. 3. 4. 5. cost; size and scalability; connectors; and noise immunity; throughput and bandwidth 59 Costs • Generally, the better the performance the greater the cost. • Economic factors such as availability, shipping, warranties and the competitiveness of the marketplace. • Installation costs are primarily based on the difficulty of installation for cable, connectors and other elements such as racks, conduit, etc... . Installation is typically the greatest cost. • Manufacturing costs include complexity of the cable and the price of raw materials such as copper and fiber. • Must find balance between cost and needs (current and future). 60 Size and Scalability • The number of nodes, the distances between the nodes and other physical constraints will determine the type of cable and how the installation is structured. • Future intentions for growth (Moves, Adds and Changes), and bandwidth requirements, both current and future, will also have an impact on the decision. 61 Connectors • Connectors are based on the type of cable used and are a large part of the cost of installation. Connectorization must include testing (and certification to standards). • A decision can be made to install extra cables (or extra strands of fiber) for termination in the future. 62 Noise • Noise immunity is the cable’s ability to deter noise (EMI and RFI) that can distort data signals. • Noise in the environment can affect the selection of cable types. 63 Throughput • Throughput is the amount of data that media carries during a given period and is measured in megabits per second (Mbps) or megabytes per second (MBps). • It is a rate but is often referred to as a “speed”. • In data communications, throughput is often referred to as bandwidth. 64 Bandwidth • In digital communications, bandwidth is defined as the transfer capabilities of the media and is also referred to in bits per second. It is a measure of the media’s capacity, cited as a maximum. • In the Analog world bandwidth has a different definition from the digital communication world. Bandwidth is the difference between the highest and lowest frequency that a media can carry, measured in Hertz (Hz). 65 Bandwidth versus Speed • The time it takes for a signal to go from the input to the output is called the velocity of propagation. The speed of a cable (how fast a signal goes from one end to another) is generally unrelated to its bandwidth. • Relative velocity of propagation (in % speed of light): ▫ Coax 85% ▫ UTP 68% ▫ Fiber Optics 66% ▫ Basic Control Wire 54% 66 Throughput vs Bandwidth • Throughput and Bandwidth are similar terms. Both have the same measurement unit, a bit rate, but bandwidth is the theoretical maximum rate whereas throughput is the actual bit rate achieved. • Consumers usually refer to transfer rates as “speed”. Although this is incorrect, the concept of throughput and bandwidth are perhaps a little too difficult to explain to the average user. 67 Baseband versus Broadband • Baseband: operate at a single frequency. Most data communication networks are baseband. • Broadband: many communication signals at various frequencies are present at the same time. Mass communication systems operate as broadband. Examples include the television channels present on a coaxial cable. Tuner 68 Bandwidth • In terms of cable selection, the bandwidth is an important consideration for cable performance. • Issues to address regarding bandwidth includes the current and future uses for the network. Data Voice Video Combination 69 Communications Cable Types 70 71 Unshielded Twisted Pair (UTP) Image: Wiki CC 72 Unshielded Twisted Pair UTP is the most common type of network cabling used today. Advantages: ▫ ▫ ▫ ▫ ▫ Standards-Based Inexpensive Flexible Universal Small Diameter Disadvantages: ▫ Limited performance over distance ▫ Installation-related factors affect performance ▫ Bandwidth limitations ▫ Susceptible to Noise 73 Unshielded Twisted Pair- Construction • Pairs of twisted insulated conductors in an overall jacket. • Configured in 4 and 25 pair configurations for structured cabling. ▫ 23 or 24 AWG solid bare copper for fixed installations. ▫ 24 or 26 AWG stranded bare copper for patch cords. • Configured in other pair counts for voice applications, commonly referred to as PIC (Plastic Insulated Conductor): ▫ 1, 2, 4, 5, 6, 8, 12, 25, 50, 75, 100, 150, 200, 300, 400, 600, 900, 1200, 1500, 1800, 2100, 2400, 2700, 3000, 3600 and 4200 pairs. 74 Twists • Lay: The number of twists per length. • Each pair must have a different lay to reduce crosstalk. Generally, the more twists per foot for the conductors, the better the performance of the cable. Lay 1 ft 75 ScTP and STP • Shielded twisted-pair (STP) ▫ consists of individually insulated twisted pairs surrounded by a metallic shielding that must be grounded. ▫ Although a high performance cable, it has disadvantages and is not in the current cabling standards. • Screened twisted-pair (ScTP) ▫ consists of insulated pairs of wires contained in a full foil laminate shield ▫ superior immunity to radio frequency fields and reduced crosstalk ▫ may be included in future TIA/EIA standards 76 UTP Categories • UTP cable is classified into performance-based categories. • The specifications for the categories are defined in the TIA/EIA 568C standard. • Categories are added to and removed from the standard as technology changes and improves. 77 Categories Category Data Rate (Mbps)1 Comments 1 0.02 Telephone and Signal Wire 2 4 Early Token Ring networks 3 10 10Mbps Ethernet, still frequently used for telephone-only installations (residential) 4 20 Latter Token Ring networks. Short-lived Category. 5 100 100Mbps (fast) Ethernet, ATM. Not recommended. 5e 100 Improved performance over Cat 5. Recommended. 6 1000 6a 10,0002 7 ? Gbts Ethernet . Recommended. Recommended for new installations but expensive and thicker. In discussion and lab testing. Likely ScTP with individually shielded pairs or conductors. 1-Mbps = Mega bits per second, or 1 million bits per second. 2- Only achievable over considerably shorter distances 78 Mbps versus MHz • Mega bits per second and Mega Hertz are different. • Ethernet data is encoded and the data doesn’t produce only two logic levels. This encoding reduces the frequency required to carry the data. • 100Mbt Ethernet operates at an average frequency of approximately 32MHz 79 Future - Twisted Pair • Category 7 ▫ 1GHz (Cat 6 = 250MHz, Cat 6a = 500MHz) Currently in discussion. Requires a fundamental cable structural change (UTP has achieved its limit with Cat 6/6a). Will need a new connector. Class ‘F’ in Europe. • SOHO - Small Office Home Office ▫ Standardization of cabling for the private sector- 4 pair balanced copper- may combine data and multimedia50 meters- 1.2 GHz • Category 8 ▫ Not determined. Likely individual shielded twisted pair with an overall shield 80 Future – Twisted Pair • Changes that may take place: ▫ Shielding Overall, individual pairs or individual conductors May have a separate drain wire ▫ Distance May decrease the maximum distances ▫ Increased wire gauge Reduced resistance ▫ Increased size Better and thicker insulation (dielectric); may require separator between pairs ▫ Different connector style (TERA, GG45 in Europe) 81 TERA and GG45 connectors. The TERA connector may be used for broadcast applications; the GG45 is backward compatible with the 8pos mod plug 82 PIC Cable • • • • Unshielded twisted pair Plastic Insulated Conductor Used for voice and low frequency communications Does not perform within the Categories range and is outside the cabling standard • Can have very large pair counts (up to 4200) • May be used indoors and outdoors (aerial or buried) 83 UTP Color Code 84 Twisted Pair – Cable Colour Code • There are five (5) primary colors and five (5) secondary colors for multi-pair cable. ▫ TIP: Secondary color with a band of Primary colors. White - Red - Black - Yellow - Violet ▫ RING: Primary color with a band of secondary colors. Blue - Orange - Green - Brown - Slate Important 85 White Pair Tip Ring 1 White/Blue - Blue/White 2 White/Orange - Orange/White 3 White/Green - Green/White 4 White/Brown - Brown/White 5 White/Slate - Slate/White 86 Red Pair Tip Ring 6 Red/Blue - Blue/Red 7 Red/Orange - Orange/Red 8 Red/Green - Green/Red 9 Red/Brown - Brown/Red 10 Red/Slate - Slate/Red 87 Black Pair Tip Ring 11 Black/Blue - Blue/Black 12 Black/Orange Orange/Black 13 Black/Green - Green/Black 14 Black/Brown - Brown/Black 15 Black/Slate - Slate/Black 88 Yellow Pair Tip Ring 16 Yellow/Blue - Blue/Yellow 17 Yellow/Orange - Orange/Yellow 18 Yellow/Green - Green/Yellow 19 Yellow/Brown - Brown/Yellow 20 Yellow/Slate - Slate/Yellow 89 Violet Pair Tip Ring 21 Violet/Blue - Blue/Violet 22 Violet/Orange - Orange/Violet 23 Violet/Green - Green/Violet 24 Violet/Brown - Brown/Violet 25 Violet/Slate - Slate/Violet 90 91 UTP/PIC Color Code TIP RING White Red Black Yellow Violet Blue Orange Green Brown Slate Pair 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Tip White Red Black Yellow Violet Ring Blue Orange Green Brown Slate Blue Orange Green Brown Slate Blue Orange Green Brown Slate Blue Orange Green Brown Slate Blue Orange Green Brown Slate 92 Binders • Cables of 50 pair and larger are grouped in 25 pair units and each wrapped with colored tape to form “binder groups”. • The binder groups (colored tape) follow the same color code as the ring wire of each pair (ie 1st binder is blue/white. ) • See lab exercise for more information. 93 Coax Cable Jacket Braid Shield Foil Shield Dielectric Image: PRGodin Central Conductor 94 Coaxial Cable Construction • An inner copper conductor carries the data • An insulating material called the dielectric holds the center conductor. The dielectric has good electrical properties. • A braided metal shield serves as a signal ground and also helps retain the shape of the cable. A foil shield in some cables offers more noise protection • An overall jacket protects the cable and has markings. 95 Advantage of Coax • There are fewer frequency restrictions with coaxial cable • All of the signal is contained within the coaxial structure. Noise emissions is less of an issue. • External noise is significantly reduced by the shield. • The impedance is relatively stable. • Can transmit much higher frequencies than UTP • Velocity of Propagation typically 85% • Relatively easy to connectorize. 96 Disadvantages of Coax • The shield of the coax, used as a reference voltage, carries noise. • Coax cable shields must be grounded properly. • Not as adaptable to use for as many systems as UTP. • Generally not as flexible. • Coax in data communications may make a comeback but is outside of the standards at this time. 97 Review Questions • What term is used to describe the data carrying capability of a communication cable? • What factors help determine cable selection? 98 Cables and Cabling Infrastructure Part 3 – Technical Cable Performance ©PRGodin @ gmail.com Updated Dec 2013 99 Electrical and Physical Specifications • Copper cables such as UTP and Coax have several important specifications that must be considered. • Technical performance issues include: ▫ Impedance (resistance, capacitance, inductance) ▫ Noise, shielding and grounding 100 Voltage, Current and Resistance • Voltage can be defined as the degree of attraction between electrons and positive ions. Can be described as “pressure”. • Current can be defined as the amount of electrons that are flowing. • Resistance can be defined as an opposition to the flow of electrons. Resistance causes voltage (“pressure”) drops. 101 Basic Model of an Atom Electron (-) Proton (+) Neutron (no charge) Nucleus Orbit (path of the spinning electrons) Basic Model of Current and Voltage Electron Hole (+) Electron (-) Force of attraction (Voltage) Flow (Current) Positive Ion V IR Basic Model of Ohm’s Law Electron Hole (+) Electron (-) Force of attraction (Voltage) Flow (Current) Resistance to flow (Resistance) Positive Ion V IR Basic Digital Signals • Basic systems work in a BINARY format ( a “1” or a “0” ) • Represented as a square wave (“+voltage” or “-voltage” over a period of time) • Signal must be above a threshold voltage to represent one binary value and below a threshold voltage to represent the other. • Signal timing must be within a threshold for each bit to be recognized. +Voltage Minimum Threshold Unknown Zone Maximum Threshold - Voltage Timing 105 Basic Digital Signal Problems • • • • Noise (unwanted signal) Impedance (reduced voltage) Capacitance (timing errors) Resistance (reduced voltage) 106 AC Signals • The varying voltage values of a communication signal are known as AC (Alternating Current). ▫ Sometimes referred to as varying DC, modulated DC or other term • AC signals may take various shapes. ▫ For digital communications they generally take on square shapes ▫ For analog communications such as in broadband they are generally sine shapes 107 Resistance • Resistance is the opposition to current flow. • Resistance is present in all conductors. • Resistance causes voltage drops in cable. • Increasing the size of the conductor decreases resistance. 108 Resistance • Symbol: • Letter Symbol: R • Unit of Measure: Ohms (Ω) ▫ Typical: Ω, kΩ Resistance of Conductors Conductor resistance in circular copper conductors AWG Ω per 100ft (30.5 meters) 12 0.16 14 0.26 16 0.41 18 0.65 20 1.04 22 1.65 24 2.62 26 4.16 28 6.62 30 10.52 110 Induction • Inductance ▫ Can be defined as the transference of electrical energy from one conductor to another. • Faraday’s law (1831) ▫ The voltage induced in a conductor is proportional to the rate of change of magnetic lines of force that pass through the conductor. Faraday’s discovery of the relationship between electricity and magnetism is often cited as the most important discovery of the modern era. 111 Magnetism • Principle: ▫ Magnetic flux lines are established between the 2 poles of a magnet ▫ The quantity, density and length of these lines increases with: N S the characteristics of the medium the strength of the magnet Image: PRGodin 112 Electromagnetism • Principle: ▫ Magnetic flux lines are established when current flows in a conductor ▫ The quantity, density and length of these lines increases with current. ▫ The direction of the flux lines is determined by the direction of the current. Image: PRGodin 113 Electromagnetism • Principle: ▫ If conductors are coiled, the flux lines of the individual turns combine and concentrate to create a bar magnet. ▫ If AC current is applied, the polarity of the magnet will reverse N S Note it takes time for the field to collapse and re-establish itself in the other direction. Inductance impedes current flow (XL). The effects of inductance increase with frequency. Image: PRGodin 114 Electromagnetic Induction • Principle: ▫ Magnetic flux lines crossing a conductor will induce current. ▫ There must be relative motion, produced with AC. ▫ The quantity of lines that cross the conductor over a period of time will determine the induced current. ▫ The direction of the current is based on the polarity and direction of the flux lines. Image: PRGodin Source Current Induced Current 115 Induction and Noise • The relative motion of the electromagnetic field occurs when fields build up and collapse with AC signals. • Inductance causes problems with communication cabling: ▫ External sources of noise (ingress) ▫ Adjacent sources of noise (within the cable) ▫ Generate noise (egress) 116 External Source: Ambient Noise • Ambient Noise: ▫ Background, steady, predictable noise. ▫ Measuring the frequency of the noise may help determine the source. 60Hz = lighting, motors, electrical appliances, electrical cabling, transformers, etc… 100Hz to 20 MHz = switching power supplies, electronic devices, telephone systems, video, etc… > 20MHz = radio transmitters, cellular telephones, etc… 117 External Source: Transient Noise • Transient Noise: ▫ Irregular and unpredictable noise. ▫ Transient noise is often difficult to pinpoint. ▫ Likely sources are switching circuits, such as Elevators, photocopiers, welders, electrical storms, static electricity, switching highcurrent devices, etc… 118 EMF, EMR, EMI, RFI and EMP • EMF and EMR: ▫ Electro-Magnetic Field and Electro-Magnetic Radiation, generally describes the strength of a magnetic field and its ability to induce current. ▫ May also refer to Electro-Motive Force (Voltage) • EMI and RFI: ▫ Electro-Magnetic Interference and Radio Frequency Interference describe undesired, induced electrical current. RFI applied to higher frequencies. • EMP: ▫ Electro-Motive Pulse which is a sudden but short-lived increase in EMI or RFI. Often destructive. EMP sources include electrical storms, solar storms and weapons. 119 Twisted Pairs and Noise • One conductor of a pair carries a signal and the other is that signal’s reference. This serves to reduce the effect of noise (Differential Voltage/Signaling) • Two pairs are needed to communicate ▫ Transmit pair ▫ Receive pair 12V V 12V V Voltage induced on both conductors Image: PRGodin 120 Noise on Twisted Pairs • Principle: If noise is induced on one conductor, the same amount of noise is induced on the other conductor. The voltage between the two conductors remains the same. Differential signaling systems have a built-in cancellation effect. 10V +12.5V +2.5V Input 5V 5V -2.5V Voltage induced on both conductors Output +7.5V Image: PRGodin 121 Internal Source: Crosstalk • A regular source of noise is CROSSTALK, where within a cable, one pair of signal-bearing conductors induces a signal on an adjacent pair of conductors. 122 Internal Source: Crosstalk • Near End Cross Talk (NEXT) is a measurement of transference of signal from one pair to adjoining pairs. • It’s measured from the same end (near end) as where the test signal is being injected. Crosstalk Image: PRGodin 123 Alien Crosstalk • Alien crosstalk is noise from an adjacent communication cable. • Bundles of UTP cable can create alien crosstalk. • Recommendations are to not bundle too many cables together for too long a distance, or too tightly. Image: PRGodin 124 Capacitance • Capacitance is storage of an electrical charge, measured in Farads. • It is a property where two conductors separated by an insulator can store an electrical charge if a voltage difference exists between them. • Capacitors are based on electrostatic principles where a force of attraction or repulsion exists between charged bodies. 125 Electro-statically charged particles Image: PRGodin 126 Electronic Capacitors • Electronic capacitors consist of two conductors usually in the form of plates, separated by an insulator (dielectric). Image: PRGodin • Increasing the plate size can be accomplished by rolling it up into a smaller package, or stacking plates. 127 Wires as a Capacitor Conductor --- --- --- --- Insulation Attraction Insulation +++ +++ +++ +++ Conductor The charge is held on the wires because the different charge polarities are electro-statically attracted to each other. Without a conductive path connecting them, the charge remains on the conductor. Image: PRGodin 128 Factors Affecting Capacitance Conductor Length (Plate size) ▫ Longer conductors means more charge can be held and higher capacitance. Separation between the conductors ▫ Larger separation between the conductors means less electrostatic attraction and lower capacitance. The Insulator ▫ The insulating material between the conductors affects the attraction and capacitance. PVC and other plastic materials have lower capacity to concentrate electrostatic fields and hold a charge. 129 Factors Affecting Capacitance Permittivity is the ability of a material to concentrate electrostatic flux. Measured and reported as dielectric constant. εr Dielectric Vacuum 1.0 Air 1.0006 Polyethylene 1.7 to 2.6 Teflon (FEP) 2.1 Polypropylene 1.5 to 2.3 Rubber 3.0 PVC 3.5 to 8 Polyurethane 7.1 Water 80.0 Sulfuric Acid 84-100 Relative permittivity of materials (symbol ε, unit F/m) The lower the value the lower the capacitance. 130 High and Low Capacitance ++++++++++++++ Conductor +++++++++ Dielectric and Electrostatic field --------------High Permittivity High Capacitance Image: PRGodin Conductor --------Low Permittivity Low Capacitance 131 Capacitance • Symbol: • Letter Symbol: C • Unit of Measure: Farads (F) ▫ Typical: µF, ηF, ρF 132 Effect of Capacitance on Cable • Capacitance causes signal deformation Original Signal Distorted signal due to capacitance • The effects of capacitance increase with frequency. Capacitance is the greatest limiting factor for high frequency performance. Image: PRGodin 133 Reasons for Twists • Reduces Crosstalk (the infringement of the signal from one wire pair on another wire pair’s signal). • Reduces Capacitance (the opposition to voltage changes). • Improves Impedance (opposition to current) • Each pair has a different lay, reducing the amount of direct contact between conductor pairs, therefore reducing capacitance and crosstalk. A divider may be present to keep the pairs separated. Same lay = Regular contact Cross-section of Cat 6 with divider Different lay = Less contact Image: PRGodin 134 135 Noise Emissions • The FCC (USA) has expressed concerns over cable emissions (called ‘cable egress’). These emissions may affect other communication systems. • Emissions are a data security risk. Signals may be picked up and deciphered. • Emissions are a loss of signal power. 136 Grounds • A ground is a point or conductor that has zero electrical potential, and is a reference point for signals. • Grounds are important for signal transfer and for safety. Grounds must be properly configured and used. • Grounding is addressed in the TIA/EIA 607 standard. 137 Ground Types • There are 3 basic types of grounds in electrical systems: ▫ Earth ground: primary role is safety. It is also the absolute reference point for voltage. The potential of an earth ground is considered 0 Volts. ▫ Chassis ground: usually used for safety and for cable shielding. Has a potential of 0 Volts. ▫ Common ground: a point of reference for signals and voltages. Not for safety. May have potential to other grounds. Chassis Ground Earth Ground Common Ground 138 Minimizing Noise • Maintain electrical separation between the communication cable and electrical appliances and conductors (addressed in the standards). • Employ shielded cable that is properly grounded. 139 Grounding and Shielding Electromagnetic Field Metallic Shield Induced Current Improper grounding and shielding is a common source of error in data cable installations. 140 Error: Ground Loop • Ground Loops are multiple paths to ground. • Ground loops interfere with the effectiveness of a ground. ▫ The different grounds may be at different potential, drawing current through the shield. ▫ The voltage reference may not be at 0 Volts. ▫ Greater issue with coax cable Other equipment Metallic Shield Current Example: One ground connection has more resistance than the other. Any equipment on the ground system may use the cable shield as a path to the lower resistance ground, creating noise on the cable. 141 Ground Potential Difference Building frame System 1 System 2 Building frame • Ground potential differences cause serious data communications problems. Here is an example: ground resistance Actual problem encountered in Calgary 142 Grounding and Shielding • Maintain a Single Ground Point Metallic Shield Induced Current Proper Ground Connection 143 Grounding and Shielding • Outdoor cable plants (OSP) require two or more connections to ground ▫ Safety overrides communication quality issues ▫ Reduce problems by using low resistance ground connections ▫ Follow engineering guidelines Metallic Shield Induced or Direct Current Proper Outdoor Ground Connections 144 Reducing the Effect of Noise (1) • Distance: ▫ Magnetic flux lines are less dense with distance from the source. Maintain a separation from any sources of noise, especially electrical cables. Addressed in the TIA/EIA 568C standard. ▫ Reduce the length of cable • Shielding: ▫ Employ shielded cable to either protect its conductors from EMR, or reducing its emissions of EMR. ▫ Employ proper ground connection techniques. Low resistance path to ground 145 Reducing the Effect of Noise (2) • Other: ▫ Use better quality cable highest category for UTP better shield coverage (other) ▫ Use the proper terminators if required ▫ Employ proper installation techniques 146 Questions • What is the difference between capacitance and inductance? • How do the plastic insulators contained within a cable affect its signal performance? • How does the structure of a cable affect its performance? 147 Impedance of a Cable • • • • Cables contain Resistance, Capacitance and Inductance. The total of these effects is called impedance. Impedance is the resistance to alternating current. The symbol is Z, the units are Ohms (Ω). Electrical equivalent of a Cable 148 Cable Impedance • The structure of the cable, its conductors plus the dielectric determine the Characteristic Impedance of a cable. ▫ For coax, typical values are 50, 75, and 93 ohms ▫ For UTP, typical value is 105 ohms ▫ Other cables will have different values • It is very important to match the impedance of the coax cable to the system requirements. Signal reflection will result in poorly matched cables. 149 Coax Cable Impedance Designation Z (Ω) Applications Comments RG58 /U or A/U 50 General instrumentation, Arcnet Solid conductor, large variety of configurations RG58 C/U 50 Ethernet Thinnet Stranded conductor, Foil/braid shield RG59 75 Video, CATV, Broadband Solid conductor RG6 75 Video, CATV, Broadband Solid conductor, better performance than RG59 RG8 50 Ethernet Thicknet Double layer of shielding, 12 AWG center conductor RG62 93 IBM 3270, Arcnet Air dielectric RG22 B/U (Twinax) 95 IBM 3X/AS400 Two conductors in dielectric 150 Reflection: Line Noise • If the transmission line are not properly impedancematched to the system, some signal reflection will occur. • On some cables (especially coax), if a terminator is not present, the signal will reflect from the end of the conductor, resulting in ringing. This echo causes interference on the cable. Image: PRGodin 151 Review Questions (1) • Define the following terms: ▫ Attenuation: ▫ Bandwidth: ▫ Digital: ▫ Impedance: 152 Review Questions (2) • Define the following terms: ▫ Ohm ▫ Amps ▫ Resistance ▫ Lay Length 153 Review Questions (3) • Define the following terms: ▫ Capacitance ▫ Inductance ▫ Crosstalk ▫ Ambient ▫ Transient 154 End of Part 3 ©PRGodin, Calgary, AB, Canada Updated Dec 2013 155