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ICTCBL3013A Perform cable and system tests on customer premises Student Workbook Student Workbook ICTCBL3013A Perform cable and system tests on customer premises 1st Edition 2010 Part of a suite of support materials for the ICT10 Telecommunications Training Package Acknowledgement These materials were developed by Innovation and Business Skills Australia in association with the Commonwealth Government through the Department of Education, Employment and Workplace Relations (DEEWR). Copyright Statement © 2011 Commonwealth of Australia The views expressed in the copyright work do not necessarily represent the views of the Commonwealth of Australia. This work is copyright and licensed under the AEShareNet Share and Return Licence (AEShareNet–S Licence). The onus rests with you to ensure compliance with the AEShareNet-S Licence and the following is merely a summary of the scope of the Licence. When you obtain a copy of material that bears the AEShareNet-S Licence mark by legitimate means you obtain an automatic licence to use, copy, adapt and/or redistribute this work. If you develop enhancements of the material, you agree that copyright in any enhancements vest automatically in the original copyright owner. Conditions for the Licence can be found at . Queries regarding the standard AEShareNet-S Licence conditions should be directed to the AEShareNet website at . In addition to the standard AEShareNet-S Licence conditions, the following special conditions apply: 1. The licence is limited to Australia and New Zealand. 2. You are entitled to charge a cost recovery fee for distribution or communication of the original work only if you are an educational provider and use the material within your organisation or use the material for the services of your organisation. Otherwise no fee may be charged. 3. If you develop an enhanced version of the material for: a. commercial distribution; you must provide a copy of the Enhanced Version and the proposed pricing for the Enhanced Version to the Commonwealth at least twenty (20) business days prior to distribution. b. non-commercial distribution (e.g. cost recovery); notification is not required. Use of this work for purposes other than those indicated above, requires the prior written permission from the Commonwealth. Requests and notification of the distribution of Enhanced Versions should be addressed to Training Copyright, Department of Education, Employment and Workplace Relations (DEEWR), GPO Box 9880 Canberra City, ACT, 2601 or email [email protected]. Disclaimer While care has been taken in the preparation of this material, DEEWR and the original developer do not warrant that any licensing or registration requirements specified here are either complete or up-to-date for your State or Territory. DEEWR and the original developer do not accept any liability for any damage or loss (including indirect and consequential loss) incurred by any person as a result of relying on the information contained in this material. The Commonwealth, through the Department of Education, Employment and Workplace Relations, does not accept any liability to any person for the information or advice (or the use of such information or advice) which is provided in this material or incorporated into it by reference. The information is provided on the basis that all persons accessing this material undertake responsibility for assessing the relevance and accuracy of its content. No liability is accepted for any information or services which may appear in any other format. No responsibility is taken for any information or services which may appear on any linked websites. Published by: Innovation and Business Skills Australia Ltd Level 11, 176 Wellington Pde East Melbourne VIC 3002 Phone: +61 3 9815 7000 Fax: +61 3 9815 7001 www.ibsa.org.au email: [email protected] First published: July 2011 Release date: 15 July 2011 AEShareNet Code: S Table of Contents Getting Started .................................................................................................................... 1 Introduction ......................................................................................................................... 3 Section 1 – Decibels and Signal Measurement................................................................ 4 What skills will you need? ............................................................................................ 4 History of bels ............................................................................................................... 4 What are decibels? ....................................................................................................... 5 Decibel millivolts (dBmV) ............................................................................................. 7 Section summary .......................................................................................................... 8 Further reading ............................................................................................................. 8 Section checklist........................................................................................................... 8 Section 2 – Testing for Satellite Antennas ........................................................................ 9 What skills will you need? ............................................................................................ 9 The importance of testing ............................................................................................ 9 Signal level meters ....................................................................................................... 9 Typical signal levels ................................................................................................... 10 How to use the results............................................................................................... 10 Section summary ....................................................................................................... 11 Further reading .......................................................................................................... 11 Section checklist........................................................................................................ 11 Section 3 – Testing Structured Cabling Systems ........................................................... 12 What skills will you need? ......................................................................................... 12 Sections of a structured cabling system .................................................................. 12 Determining cabling performance ............................................................................ 14 Structured cable tests ............................................................................................... 17 Section summary ....................................................................................................... 27 Further reading .......................................................................................................... 27 Section checklist........................................................................................................ 27 Section 4 – Testing Optical Fibre Cables........................................................................ 28 What skills will you need? ......................................................................................... 28 Testing fibre with an optical power test set ............................................................. 28 Optical time-domain reflectometers ......................................................................... 32 Typical OTDR responses ............................................................................................ 33 Losses in termination and installation of fibre optic cables ................................... 34 Section summary ....................................................................................................... 36 Further reading .......................................................................................................... 36 Section checklist........................................................................................................ 36 Student Workbook Getting Started Getting Started This Student Workbook has been developed to provide a learning pathway to competence in ICTRFN3013A Perform cable and system tests on customer premises. It contains the skills and knowledge required to achieve competence in this unit. The learning process includes:  reading and discussing the content with your instructor  discussing your experience with the content – you can apply the content in your workplace  answering simple questions both in writing and in discussion  performing simple learning activities – making calculations or handling equipment for instance  reading reference books and Australian standards. Your instructor/trainer will guide you through this learning process. Optical and RF testing Testing for optical fibre is covered in the learning resources for ICTCBL3065A and testing antenna signals is covered in the learning resources for ICTRFN3055A. Learning pathway DECIBELS AND SIGNAL MEASUREMENT TESTING ANTENNA SIGNALS LEARNING ACTIVITIES TESTING STRUCTURED CABLE TESTING OPTICAL FIBRE PRACTICAL ASSESSMENT PRACTICAL ASSESSMENT ICTRFN3013A Perform cable and system tests on customer premises ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 1 of 36 Getting Started Student Workbook Assessment tasks When you have completed the learning tasks in this guide you will be assessed on your ability to apply the learning. You will have several chances so if you are not completely successful the first time, your assessor or instructor will arrange for a resit of some or all of the assessment tasks. Page 2 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Introduction Introduction Welcome to the ICTRFN3013A Perform cable and system tests on customer premises Student Workbook. Cable system testing can cover a wide range of situations from the simplest TV or radio antenna to structured cable, coaxial cable or optical fibre. Testing will determine whether your installation has been effective and whether it is performing to the required standard. Cable testing is an important skill in the electronic communication sector. In this program we will look at some general principles of testing – particularly the concept of decibels (dB) – that you can apply to many situations and we will then focus on some specific tests. In this learning program you will develop an ability to perform simple broadband-related tests. You will learn about the following:  decibels and signal measurement  testing satellite antenna signals  testing structured cabling system  testing optical fibre systems. At the completion of this program you will have learned valuable skills in testing communications systems. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 3 of 36 Section 1 – Decibels and Signal Measurement Student Workbook Section 1 – Decibels and Signal Measurement This section is about the measurement of signals and signal loss using decibels (dB). What skills will you need? In order to work effectively as a broadband network installer and tester you must be able to:  explain the basic idea of a dB as a measure of signal gain or loss  explain how losses and gains occur. History of bels When the first telephone lines were constructed in the 19th century it was discovered that the voice signals got weaker the further they had to travel. For every 10 miles of telephone line the signal was reduced to a 10th of its original power. This loss of signal strength is called attenuation. Signal 10 % Power Out 100 % Power In 10 miles Reduction in signal power after 10 miles of telephone cable This 10 to 1 (10:1) ratio of input to output power became a standard unit of measurement, named the bel in honour of Alexander Graham Bell who is credited with inventing the first practical telephone in the 1870s. Page 4 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 1 – Decibels and Signal Measurement What are decibels? The bel experiences a 90% loss of signal, which makes it quite a large unit. Over time it became more convenient to divide this by ten giving us the unit we use today – the decibel (dB). Other measurements such as volts, amps or ohms measure a physical quantity while the decibel measures a ratio – it is comparing two different amounts at two points on a telecommunications system. The decibel measures the ratio between the power at the input of a circuit and the power at the output of a circuit. In this way decibels are used to specify a loss or gain across a circuit, regardless of what the actual level might be. 100% POWER IN 10% POWER IN 10% TRANSMISSION AMPLIFICATION POWER OUT 100% POWER OUT The decibel gives us a convenient way to specify the performance of individual components in a broadband cable network, such as cable sections, amplifiers, taps and splitters. Formula for dB (power) If you think back to the 10 miles of telephone cable with a loss of 10 dB – from this we can see that to convert our ratio of input power (P1) to output power (P2) to the logarithmic system of decibels (in this case 10 dB), we can use the following formula: In our case: ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 5 of 36 Section 1 – Decibels and Signal Measurement Student Workbook Because there are 10 decibels to one bel, we can multiply both sides of the above formula by 10, to give: In our case: Formula for dB (voltage) However, the above formula only applies to ratios of power. If we are comparing signal level in terms of voltage, we need to modify the formula slightly. If P is power, I is current, E is volts or electromotive force (EMF), R is resistance, power can be expressed as: Ohm’s law provides a formula for the current (I) showing that it is directly proportional to the potential difference in volts across the two points (E) and inversely proportional to the resistance between the two points in ohms (R). Ohm's law states that the R in this relation is constant, independent of the current. This formula is shown below. When we substitute in Ohm’s law for I, we get: If we use this equation to replace P in our formula for dB, it becomes: Page 6 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 1 – Decibels and Signal Measurement Summary  Decibels (dB) are used to measure ratios of power or voltage, not actual levels of signal.  Decibels are typically used to specify loss or gain of signal as it travels along the network.  0 dB indicates a ratio of 1:1. This means we have the same level of signal at output and input – there is neither a gain, nor a loss.  3 dB indicates a ratio of approximately 2:1. This means we have lost half the power  10 dB indicates a ratio of 10:1. In a component with 10 dB loss, only one tenth of the power appears at the output.  The formula for dB when comparing power is  The formula for dB when comparing voltage is Decibel millivolts (dBmV) To specify a gain and loss in signal strength using decibels we need a method of measuring signal level. This is where we use the decibel millivolt (dBmV). If there is a certain level of signal in dBmV, it is the ratio of the signal to the reference level which is 1 mV. To put this another way, we are saying ‘how many dBs is that signal above or below one millivolt’. dBmV examples A signal that measures 3 dBmV is 3 dB above our reference of 1 mV. This means it contains twice the power compared to 1 mV (a 2:1 power ratio). If the signal level was exactly 1 mV (a 1:1 power ratio) then the level would be 0 dBmV. A reading of 0 dBmV doesn't mean there is no signal. It means there is a good signal equal to 1 mV. To put it another way – there has been no gain or loss. If the signal level was less than 1 mV, then the level would be less than 0 dBmV; in other words a negative number. For example, if there was only half the power of 1 mV (or a 1:2 ratio) then the level would be -3 dBmV. dBmV Voltage (millivolts) Power (nanowatts) 0 dBmV 1.00 mV 13.33 nW 2 dBmV 1.26 mV 21.13 nW 3 dBmV 1.41 mV 26.60 nW 4 dBmV 1.59 mV 33.49 nW ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 7 of 36 Section 1 – Decibels and Signal Measurement Student Workbook 6 dBmV 2.00 mV 53.08 nW 8 dBmV 2.51 mV 84.13 nW 10 dBmV 3.16 mV 133.33 nW Why a 1 mV reference? The original reason that 1 mV was chosen as a reference level was the 1 mV gave good quality black-and-white reception on cable television. It is considered necessary to provide a signal of at least three or four dBmV or 1.4 to 1.6 mV for normal colour cable television. Summary  dBmV is used to measure amounts of signal level. They are what we will read on our signal level meter.  dBmV are amounts of signal with reference to a level of 1 mV = 0 dBmV It is good practice when referring to signal level (say at the output of amplifiers or taps, or into set-top units) to say ‘dBmV’ rather the abbreviating it to ‘dB’. This way there will be no confusion about whether you are referring to an amount of signal, or the loss through some passive component or cable. Section summary You should now understand what is meant be the term dB (or decibels) and dBmV (decibel mV) and what readings in dB and dBmV tell us about a telecommunications system. Further reading  vendor/supplier information.  industry journals. Section checklist You should now be able to:  explain the basic idea of a dB as a measure of signal gain or loss  explain how losses and gains occur. Page 8 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 2 – Testing for Satellite Antennas Section 2 – Testing for Satellite Antennas Broadband services are usually delivered by fibre cable or over the mobile phone network. Some customers will use satellite antenna because of their location. You may be called on to make an assessment of an antenna service to a customer. This section looks at how you might make some preliminary measurements of the performance of a satellite antenna. Testing procedures for satellite dishes receiving TV or broadband signals are very simple and require only simple equipment. What skills will you need? In order to perform simple performance tests on a satellite antenna you must be able to:  explain why you are testing the antenna  describe the function of a signal level measuring device  test for signal levels and losses Note that you may have met the requirements for this section if you have completed ICTRFN3055A Install a radio communications antenna and feedline. The importance of testing To accurately install and align a satellite dish you will need to measure the quality of RF signals the dish is receiving. These measurements are taken with a signal level meter. Signal level meters A signal level meter can be as simple as a single readout device that costs less than $10 or as complex as multifunction metres that cost hundreds or thousands of dollars. These devices are often called Field Strength Meters (FSMs). Because of the variation in these devices is not possible to give specifics on how to use each one. As a rule, once you understand the principles of measurement, you simply need to follow the instructions for the device you're using. Most measurements will be taken at the dish at the time of installation. You may also measure the signal reaching appliances – TVs or computers. Most signal level meters will take a measurement anywhere they can be coupled with a coaxial cable. Your instructor will show you one more of these metres and you will use these in your training and assessment activities. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 9 of 36 Section 2 – Testing for Satellite Antennas Student Workbook Because this is a practical task you will be relying on your instructor to demonstrate the use of this testing equipment. The two main measurements you will need to take are:  signal level in dBμV (decibel micro Volt)  carrier to noise ratio (CNR) in decibels When working with digital signals you may also need to measure:  Bit Error Rate (BER)  Modulation Error Rate (MER). Typical signal levels Typical signal levels at the satellite dish are:  signal level into satellite receiver – 58 to 75 dBμV  output level from Low Noise Block (LNB) – 75 to 85 dBμV  levels for BER should be in the order of 1:1,000,000 (one error per million bits)  CNR is usually applied to analogue signals – soon to be obsolete  MER is used in more complex functions such as evaluating the effectiveness of amplifiers. How to use the results Results of testing can be used to:  accurately align the satellite dish  identify any potential faults in the dish, LNB or cabling leading to appliances. Your instructor will demonstrate the use of one or more signal level metres (depending on enterprise policy) and the application of this data to satellite alignment and cable testing. Learning activity: Testing antenna alignment You may have completed similar tasks as part of your antenna installation training. If so, discuss whether you need to complete this a second time. You will conduct a simple test on an antenna to determine if it is properly aligned. If it is not you can either re-align it or report your findings to your instructor. 1. Obtain a signal level meter and ask you instructor to explain its operation if it is not one you have used before. Ideally you should be using the same meter the instructor explained and demonstrated during the training session. 2. Organise access to the antenna ensuring all safety requirements are met. Complete a job safety analysis, if you are not sure. Page 10 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 2 – Testing for Satellite Antennas 3. Obtain and record signal strength at readings the antenna and compare them with recommended levels. 4. Organise access to cable terminations inside the customer premises and take signal readings. 5. Identify any significant differences and either rectify the fault or recommend action to your instructor. 6. Document readings and actions. 7. Reinstate site. Section summary You should now be able to take simple signal strength measurements for a satellite antenna. Further reading  vendor/supplier information.  industry journals. Section checklist You should now be able to:  explain why you are testing the antenna  describe the function of a signal level measuring device  test for signal levels and losses. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 11 of 36 Section 3 – Testing Structured Cabling Systems Student Workbook Section 3 – Testing Structured Cabling Systems For customers using the broadband network, structured cable will be the most common link between the Optical Network Terminal (ONT) and their end-user hardware such as computers, phones and other equipment. In this topic we take an overview of structured cable systems and gain some important experience in handling structured cable systems and performing some simple tests. This section is about structured cable – its features, functions and testing methods. What skills will you need? In order to work effectively as a broadband network tester you must be able to:  identify and explain the structure and function of structured cable  apply testing procedures and analyse the results. Sections of a structured cabling system The term ‘structured cabling’ usually refers to a multi-outlet building or campus telecommunications cabling system. It is based on the use of twisted pair cable containing four pairs and referred to as Category 5 (Cat 5), Category 6 (Cat 6), etc. Think of a multi-storey office building. Its structured cable system can be broken up into four sections: 1. Workstation section – consists of cords, adaptors and any other transmission equipment that allows for the connection of PCs, peripherals and other equipment. 2. Horizontal cabling section – this is the RJ45 outlet and the required cable connecting the work station to the telecommunication cabinet. This includes jumpers or patch cords at the distributor or consolidation point. There are normally two outlets per workstation. 3. Backbone cabling – this is the cable that provides the connection for multiple circuits between the central equipment and other locations whether it be between buildings, between floors (riser) or between two distinct locations. If copper is used the total distance must be limited to 90 metres. With single-mode optical fibre going this can be extended over many kilometres. 4. Equipment room section – this is made up of the transmission equipment, patch leads and connecting hardware used to connect the common equipment to the cabling network. Page 12 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 3 – Testing Structured Cabling Systems This linear model (above) can be expanded to show some of the complexity as the system is distributed to various termination points (terminals). A hierarchy emerges in the structured cable system, as shown below. The terms used in these diagrams mean: CD – Campus distributor BD – Building Distributor CP – Consolidation Point TO – Telecommunications Outlet ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 FD – Floor Distributor Page 13 of 36 Section 3 – Testing Structured Cabling Systems Student Workbook Learning activity: Structured cabling systems In reality a structured cable system plan is more like the diagram below with multiple pathways and jumper points. Can you identify where the Telecommunications Outlets (TOs), Floor Distributers (FDs) and the Campus Distributer (CD) are located in the diagram above? Determining cabling performance Insertion loss Insertion loss is the total signal loss of the cable including the mismatch losses at the input and output of the cable. The longer the cables run – the higher the losses. This is one factor that restricts the length of structured cable that can be used to 90 metres in a structured cable system. The higher the signal frequency – the higher the losses. This compounds the effect of insertion loss over long cables. Cable Larger Input Signal Page 14 of 36 Smaller Output Signal ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 3 – Testing Structured Cabling Systems Return loss Return loss is the addition of all reflections along the cable. When a signal is sent along the cable, a smooth passage is required for the maximum power to be received at the far end. A smooth flow of signals requires that the equipment cords, patch leads, cable and other components must have matching impedance (balancing input and output impedance). Reflections occur along the cable due to poor installation methods such as having too small a bending radius, kinks in the cable, stretching of the cable and compressing the cable with cable ties that are too tight. The effect of all the above will increase the internal noise level of the cable until the receiver cannot understand the signal. Nominal velocity of propagation and length of cable Two line constants which slow down the speed of signal along the cable are ‘series inductance’ and ‘shunt capacitance’. Velocity of propagation is the speed of light in free space so the slower speed of the signal with the cable is expressed as a percentage of the speed of light and is known as the nominal velocity of propagation (NVP). Before a test is carried out on a cable it is essential that the tester is set to the NVP of the cable. To determine the length of the cable the tester must calculate the time it takes for the signal to reach the far end of the cable and be reflected back along the cable to the tester. As you can see from this, the NVP of the cable is critical to the accuracy of the test results. Typical values of NVP in cables vary from 65% to 70% of the speed of light depending on the manufacturer. It is therefore essential that you find out this detail from the manufacturer before starting the test. Crosstalk When a signal is sent along a pair in a multi pair cable the inductive coupling between the pairs causes signal to appear in adjacent pairs causing noise. This noise is known as crosstalk. There are a number of crosstalk measurements taken when testing the installed cable. These are: 1. Near end crosstalk (NEXT) 2. Far end crosstalk (FEXT) 3. Attenuation to crosstalk ratio (ACR) ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 15 of 36 Section 3 – Testing Structured Cabling Systems Student Workbook 4. Power sum near end crosstalk (PSNEXT) 5. Power sum far end crosstalk (PSFEXT) Near end crosstalk NEXT is the internal noise created on adjacent pairs at the same end as the injected signal due to inductance. This usually is greatest within the first 20 metres. Inductance increases with the rate of change in the signal therefore the crosstalk is greater with the increase in frequency. NEXT is read at the communication room end of the cable. The twist ratio of the pairs within the cable is designed to reduce crosstalk. The twist ratio is different for each pair. Poor installation practices that do not keep the correct bending radius, and kinking or squashing the cable will alter the twist ratio and therefore cause additional crosstalk. Far end crosstalk FEXT is measured at the workstation end of the cable. The signal is injected at the communication room end and it appears as interference in adjacent pairs along the total length of the cable not just in the first 20 metres as in NEXT. Other crosstalk measurements The other measurements listed can be taken with commonly used measuring equipment. Their technical explanation goes beyond the scope of this course. Characteristic impedance Characteristic impedance is determined by the series inductance and the shunt capacitance of the cable. The nominal characteristic impedance in a structured cable system is 100 ohms for UTP or STP cable. The physical dimensions of the twisted pair that determine the characteristic impedance are:  wire diameter  insulation material used on each wire  distance between the wires. These dimensions are critical in the manufacture of the cable so the proper installation of the cable is also critical to maintain the transmission properties of the cable. Stretching, kinking, too small a bending radius and over-tightening cable ties will alter the physical properties of the cable and therefore change the characteristic impedance which, in turn, will change the transmission quality. The characteristic impedance of twisted pair copper is shown in the diagram below. Page 16 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 3 – Testing Structured Cabling Systems Wire spacing Copper Wire Insulation If the conductor spacing and wire size are constant along the entire length of the cable then the signal will find a constant impedance and it will be sent efficiently and with maximum transfer of power from the input to the receiver. Structured cable tests Tests on structured cable systems are conducted with a cable test set. There are a number of commercially available test sets. Each has its own unique features and settings. It is beyond the scope of this unit to explain the operation of each structured cable test set. What we can do here is look at some of the principles on which these test sets operate and outline some of the tests you may be required to perform. When employed in the industry, your employer will nominate a specific type of test set for you to use. You can develop your ability to use a specific test set by combining this general training with enterprise specific training and the equipment manuals supplied with the test unit. Overview of structured cable testing There are two alternative tests in the menu of the tester: 1. The permanent link test checks the performance of the installed cabling. It tests the fixed cabling and the terminations. 2. The channel test checks the overall cabling including the patch leads and the cross connects and fly leads connecting the equipment at the workstation. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 17 of 36 Section 3 – Testing Structured Cabling Systems Student Workbook The diagram below shows where these tests are performed on a structured cable system. Maximum lengths of cable for permanent link and channel For a permanent link, the maximum length is 90 metres at 20°C and has to be de-rated if the ambient temperature is higher. For a channel, the maximum length is 100 metres including 10 metres of patch cable and fly leads. Test sets Test sets can perform a number of tests, some of which are listed below. Field certification test set parameters must meet the standards as set out in AS/NZS ISO/IEC 61935.1 Testing of balanced communication cabling in accordance with ISO/IEC 11801 – Installed cabling. Once calibrated for the standard, most test sets will perform a complete suite of tests automatically and give a simple summary of the results. The following tests will normally be completed:  length  DC loop resistance  wire map  delay skew  insertion loss (IL), previously known as attenuation  near end crosstalk (NEXT)  far end crosstalk (ELFEXT)  power sum NEXT loss (PSNEXT)  return loss (RL)  attenuation to crosstalk ratio (ACR). Some of the tests are explained below. Remember that most of these tests are performed automatically by the test set. Your task is to interpret the results which appear in the tester page ‘summary results’. This summary results page will be examined in detail later in this chapter. Page 18 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 3 – Testing Structured Cabling Systems Length This test is performed using the NVP function of the test set. The instrument sends a pulse down the cable and measures the length of time to receive a reflection from the far end and by using a mathematical calculation works out the length of the cable. DC loop resistance This is a measurement of the resistance of the cable pairs looped at the distant end. Each pair is measured and will give a different result. This is due to the difference in twist ratio of each pair. Wire map A wire map test proves that each wire is terminated in the correct pin position at each end of the cable including the screen if provided. Delay skew Propagation delay is the time taken for a signal to travel the length of the cable. As all the cable pairs have a different twist ratio then the different length of each pair will give a different delay time for the signal. This is called delay skew. Insertion loss Insertion loss is a measure of signal loss in the permanent link or channel. The term ‘attenuation’ has been used to designate insertion loss. Insertion loss is tested from 1 MHz through 250 MHz in maximum step size of 1 MHz. It is preferred to measure insertion loss at the same frequency intervals as NEXT loss in order to provide a more accurate calculation of the attenuation-to-crosstalk ratio (ACR) parameter. Tester set summary results – minimum test results documentation: The test results for the worst wire pair must show the highest attenuation value measured (worst case), the frequency at which this worst case value occurs, and the test limit value at this frequency. Near end crosstalk (NEXT) ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 19 of 36 Section 3 – Testing Structured Cabling Systems Student Workbook Pair-to-pair NEXT loss is tested for each wire pair combination from each end of the link (a total of 12 pair combinations). This parameter is measured from 1 through 250 MHz. NEXT Loss measures the crosstalk disturbance on a wire pair at the end from which the disturbance signal is transmitted (near-end) on the disturbing pair. The maximum step size for NEXT loss measurements shall not exceed the maximum step size defined in the standard. NEXT is to be measured from each end of the link-undertest. These wire pair combinations must be identified for the tests performed from each end. Tester set summary results – minimum test results documentation: Identify the wire pair combination that exhibits the worst case NEXT margin (2) and the wire pair combination that exhibits the worst value of NEXT (worst case). Each reported case should include the frequency at which it occurs as well as the test limit value at this frequency. Far end crosstalk FEXT measurements are taken at the far end of the cable as shown above and evaluated in the same way as NEXT. Power sum NEXT loss PSNEXT Power sum NEXT loss is evaluated and reported for each wire pair from both ends of the link under test. PSNEXT loss captures the combined near-end crosstalk effect on a wire pair when all other pairs actively transmit signals. As for NEXT this test parameter must be evaluated from 1 through 250 MHz and the step size may not exceed the maximum step size defined in the standard (as shown in Table 1, column 2). Page 20 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 3 – Testing Structured Cabling Systems Tester set summary results – minimum test results documentation:  identify the wire pair that exhibits the worst-case margin and the wire pair that exhibits the worst value for PSNEXT  these wire pairs must be identified for the tests performed from each end  each reported case should include the frequency at which it occurs as well as the test limit value at this frequency. Return loss RL measures the total energy reflected on each wire pair. Return loss is to be measured from both ends of the link-under-test for each pair. This parameter is also to be measured from 1 through 250 MHz in frequency increments that do not exceed the maximum step size defined in the standard. Tester set summary results – minimum test results documentation:  identify the wire pair that exhibits the worst-case margin and the wire pair that exhibits the worst value for return loss  these wire pairs must be identified for the tests performed from each end  each reported case should include the frequency at which it occurs as well as the test limit value at this frequency. Attenuation to crosstalk ratio ACR is the ratio obtained by subtracting insertion loss (attenuation [dB]) from near end crosstalk (dB). ACR is normally stated at a given frequency. ACR presents an indication of quality for the circuit expressed as ‘head room’. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 21 of 36 Section 3 – Testing Structured Cabling Systems Student Workbook Alien crosstalk Alien crosstalk is a new test for structured cabling. It is measured by injecting a signal into a number of cables in a bundle and measuring the crosstalk in the cable under test. This test will be used in 10G Base T applications. Tester page summary All testers display one or two pages of test summary. The summary also shows a pass or fail result. Pass and *Pass A *Pass indicates a conditional Pass as shown by the *. This means that the test is within the accuracy of the tester and may be accepted by the customer as a Pass result. To get an unconditional Pass you may need to re-terminate the cable or check the cable run for kinks, too tight bending radius or squashed cable. Fail and *Fail A Fail indicates a check of the cable is required and faults repaired. The cable then has to be retested. A *Fail is a similar indication as the *Pass and shows that the result appears to be below the required standard and tolerance of the tester. Page 22 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 3 – Testing Structured Cabling Systems Saving test results All testers are able to save the results to the tester’s memory with full results including the graphical data. This will include the outlet identification, type of test and pass or fail result. The results can then be printed out using the instrument printer port or downloaded to a computer. Each supplier of instruments provides software for this purpose. Normally by pressing the save key the screen appears to let you record the cable identification. If the auto increment is on then the tester will automatically record the next number. Set up the test set Note: Different manufacturers’ test sets have different methods of set-up and result notification so the specific manufacturer’s instructions must be read before starting the set-up procedure. It is important to check the installation and cable type specification as to the required test. Care must be taken when handling the cords and test heads of the test set as damage to these parts will result in a faulty test. Check the battery to make sure that it is fully charged so that the full tests can be completed without problems or faulty tests. Always set the NVP to suit the cable under test. This is normally between 67% and 71% for balanced twisted pair cable. This must be correct to provide the TDR tests. Check when the tester was last calibrated to see if the latest software is installed. Note: Testers should be factory calibrated at least every 12 months. Faulty calibration and out-of-date software will result in faulty tests. Set up the test set for channel or permanent link as required by the specification. Testing Before starting the testing procedure a self-calibration of the set should be done as per the manufacturer’s handbook. Most measurements are carried out using the auto test function, which automatically completes the required series of tests for the selected test standard. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 23 of 36 Section 3 – Testing Structured Cabling Systems Student Workbook Key values for testing a balanced cable Below are some of the key values for testing a balanced cable. Compare the readings taken by your test set with these to assess a cable installation. Return loss values for channel at key frequencies Insertion loss values for channel at key frequencies NEXT values for channel at key frequencies Power sum NEXT values for channel at key frequencies Page 24 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 3 – Testing Structured Cabling Systems Learning activity: Structured cable termination and testing This exercise is designed for students to work in pairs. It is assumed that by the time you come to the training program you will have completed many hours of cabling installation as required in the open registration communication training, and understand the basic problems with cabling installation. Equipment required  RJ45 outlets  Approximately 20 metres of Cat 6 cable – 4 pair  patch panel  module suitable for a consolidation point  a level 3 tester set suitable for permanent link and channel testing. Each student will terminate structured cable on a RJ45 socket to match the category of cable being used. Procedure Working in pairs, each team is required to: 1. terminate one end of a length of Cat 6 cable – no shorter than 20 metres 2. select the correct outlet, in this case Cat 6 3. strip the sheath from the cable approximately 50-60mm from the end and remove the central spacer 4. use the 568A method – the back of the socket will usually have colour code for 568A and 568B wiring methods 5. position the sheath no more than 5-6mm from the first termination point 6. untwist the pairs one at a time and place them in the slot to match the colour 7. keep the twist ratio as close as possible to the termination point 8. terminate the wires using the manufacturer’s selected tool – always use the tool at right angles to the termination so as not to damage the terminals 9. check that the correct colour code has been used, the twist ratio has been maintained and the sheath is no more than 5-6mm from the first termination. Testing the termination Using a wire map tester: 1. check the battery is in good order 2. test the patch leads to ensure they are in good condition 3. check that all the terminations are connected correctly. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 25 of 36 Section 3 – Testing Structured Cabling Systems Student Workbook Learning activity: Structured cable installation and testing This exercise is designed for students to work in pairs. It is assumed that by the time you come to the training program you will have completed many hours of cabling installation as required in the open registration communication training, and understand the basic problems with cabling installation. Equipment required  RJ45 outlets  Approximately 20 metres of Cat 6 cable – 4 pair  patch panel  module suitable for a consolidation point  a level 3 tester set suitable for permanent link and channel testing. Each student will terminate structured cable on a RJ45 socket to match the category of cable being used. Procedure Working in pairs, each team is required to: 1. install a 24 port patch panel in a cabinet using the correct bolts and nuts, noting the space in rack units taken by the panel 2. run a 4 pair Cat 6 cable (minimum length of 20 metres) from an outlet to the patch panel 3. inspect the cable to ensure that there are no kinks or bends smaller than the recommended radius 4. terminate the cable at the patch panel in the correct manner using the manufacturer’s recommended tool 5. terminate the cable at the outlet as in previous exercise. Testing the installation Using a hand held tester: 1. check that the batteries are fully charged – if the battery is low then faulty tests will result 2. inspect the tester heads and cables to ensure they are in good condition 3. set up the tester to test a permanent link using the manufacturer’s handbook – note that some testers will cancel out the test leads when testing 4. start the auto test Page 26 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 3 – Testing Structured Cabling Systems 5. when test is finished check the results in the tester memory 6. number the cable 7. when both cables are tested and recorded, patch both cables together at the patch panels 8. test the cables from outlet to outlet using the patch panel as a CP and compare the results with previous tests. Section summary You should now understand how to work with and test structured cable systems. Further reading  vendor/supplier information.  industry journals. Section checklist You should now be able to:  identify and explain the structure and function of structured cable  apply testing procedures and analyse the results. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 27 of 36 Section 4 – Testing Optical Fibre Cables Student Workbook Section 4 – Testing Optical Fibre Cables In this section you will use a power meter and an optical time-domain reflectometer (OTDR) to test cables and diagnose faults. The power meter will be the testing device that you rely on most regularly to test optical fibre cables. Most installers will rarely use OTDRs due to their high cost and complexity. These devices will be used mainly by network engineers. An basic understanding of OTDRs is all you will need to work effectively as an installer. What skills will you need? In order to work effectively as an optical fibre cable installer, you must be able to:  test the power loss of a fibre cable with a optical power test  demonstrate the correct fibre optical characteristic trace as shown by an OTDR. Note that you may have met the requirements for this section if you have completed ICTCBL3065A Splice and terminate optical fibre cable for carriers and service providers. Testing fibre with an optical power test set An optical power test set consists of an optical source (either LED or laser) and an optical power meter for receiving the light pulse. The optical power test set is used to measure the power loss over a link of cable. Note that a cable link could consist of many splices and connector joints. Optical light source meter A light source meter is a hand-held instrument able to provide a light output within one or more of the standard windows: 850 nm, 1310 nm and 1550 nm using a LED or laser source. They often provide outputs at more than one wavelength. An installation contract may require measurements to be taken at two different wavelengths. For reliable results, the power output of the light must be very stable over a period of test, typically within 0.1 dB over 1 hour. An image of a common light source meter has been included below, manufactured by Kingfisher Australia. Page 28 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 4 – Testing Optical Fibre Cables Optical power meter At first glance, these look very similar to light source meters. They are often sold as matching pairs and there is nothing to prevent any light meter and power meter being used together, provided they are compatible. If the power source has multiple wavelengths, the power meter should also have multiple wavelengths. This allows the fibre characteristics to be quoted at any required wavelength. The power levels are normally indicated in decibels as dB, relative to one milliwatt. They are available with internal memories to store the day’s work and a thermal printer for hard copies. The power source and power meter must be calibrated by an authorised company at least every 12 months or as required by the manufacturer. An image of a common optical power meter has been included below, manufactured by Kingfisher Australia. Power measurements The test you will perform will only indicate if the power loss over a link of fibre cable is acceptable, but if an excess loss is detected, this test will not pinpoint the cause and location in the link of excess signal power loss. To determine if the measured loss is acceptable, refer to the requirements specified by AS/NZS 3080:2003/Amdt 1:2009 and/or the relevant cable supplier. There are two simple steps to perform in order to obtain the power loss measurements of a cable link. Note that all testing should be completed in both directions of the same fibre. Individual fibres are only one way traffic and at installation/testing the intended direction of use is unknown. Some faults only show up in one direction and not the other. Step One: Optical power meter calibration Because we do not connect the fibre link directly to the optical power meter, but via a pair of reference cables, we need to firstly measure the losses which are caused by the reference cables and the connectors on the meter devices. Depending on the type of power meter you are using and the type of fibre cable you are testing, refer to the user manual for precise set up procedures. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 29 of 36 Section 4 – Testing Optical Fibre Cables Student Workbook 1. Connect the power meter as in the following diagram. Connectors Light source Reference cables Power meter 2. Measure and record the losses caused by reference cables etc. Step Two: Cable link power loss 1. Connect the cable link into circuit as in the follow diagram. Cable under test Connectors Light source Reference Cables Power meter 2. Measure and record the loss now with the cable link inserted. 3. Find the difference in power loss between the calibration reading obtained in Step One and this reading. This difference will equal the loss of the cable link. Learning activity: Optical power meter testing Use light source and power meters to test three cables and answer the questions. Cable 1 Completed  1. What is the optical fibre cable type you are testing?  2. What maximum power loss reading should you read for this fibre cable link?  3. What is the calibration loss reading?  Page 30 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 4 – Testing Optical Fibre Cables 4. What is the fibre cable link loss?  5. What is actual cable link loss?  6. Is the fibre cable link acceptable?  Cable 2 Completed  1. What is the optical fibre cable type you are testing?  2. What maximum power loss reading should you read for this fibre cable link?  3. What is the calibration loss reading?  4. What is the fibre cable link loss?  5. What is actual cable link loss?  6. Is the fibre cable link acceptable?  Cable 3 Completed  1. What is the optical fibre cable type you are testing?  2. What maximum power loss reading should you read for this fibre cable link?  3. What is the calibration loss reading?  ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 31 of 36 Section 4 – Testing Optical Fibre Cables Student Workbook 4. What is the fibre cable link loss?  5. What is actual cable link loss?  6. Is the fibre cable link acceptable?  Optical time-domain reflectometers This is a device primarily used to test the optical fibre cables. An optical time-domain reflectometer (OTDR) works by injecting a laser pulse into the core of the fibre cable and detecting reflected back scattered light pulses as well as the power loss of the original injected laser signal. The return signal is displayed on the OTDR, which then allows the operator to diagnose a fault location. As well as indicating faults, the OTDR can be used to map out the construction of a cable link, to allow the operator to locate various splices/ connections and the distances to these points. A typical OTDR is pictured below. A block diagram of an OTDR has been included below to demonstrate how it functions.1 1 Reproduced with the permission of Optic Fibre Systems, viewed June 2011, . Page 32 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 4 – Testing Optical Fibre Cables An OTDR should be able to perform the following basic cabling tests.  Map the location of connectors/splices of a cable.  Indicate cable losses.  Identify cable bend radius violations, such as pressure points.  Measure cable distances. Looking back at the power meter tests, you were able to identify if a complete link of a cable had a level of power loss within specified limits, and whether you could certify the fibre cable link as acceptable or not acceptable. Remember that a cable link could contain many splice and connector joints. The limitations of the power meter test were that it could identify a faulty link, but not tell us where in the link the fault arises. But with an OTDR, it is possible to identify within two per cent of total length of the cable where the fault is located and the type of fault. The operator can then if necessary remedy the fault. Typical OTDR responses The OTDR display screen is divided up into an ‘x’ and ‘y’ axis. The ‘x’ axis represents losses, and the ‘y’ axis indicates distance. Note that as all cable have inherent losses the signal will always move in a downwards direction as the injected test laser signal travels along the cable link. As particular events are detected, the sloping signal will show different peaks rises and drops for a particular location in the cable link. An example of a graph of an OTDR trace has been included below2. It shows the following conditions: 1. Reflection from unterminated fibre. 2. Reflection from a connector. 3. Reflection from a splice. 4. Reflection from hairline crack in fibre. 2 Ibid. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 33 of 36 Section 4 – Testing Optical Fibre Cables Student Workbook 5. Backscatter. 6. Matched fibres with no reflection, but no attenuation. Losses in termination and installation of fibre optic cables This chapter identifies several key examples of the types of faults that can be identified and located by an OTDR. Angular misalignment This is caused by the connector not being faced correctly and therefore not aligning in the correct position.3 Frensel reflection This loss is caused at every connection of the fibres where some of the light source is reflected back along the fibre.4 3 Ibid. Page 34 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Student Workbook Section 4 – Testing Optical Fibre Cables Loss due to bending These losses are self explanatory. If the bend is too tight, light will be lost. The attention given to the recommended bending radius is paramount when installing fibre optic cables.5 Field termination problems In multimode fibre when the fibre is placed in the ferrule and glued, it will lie over to one side and therefore be off centre as the diagram below. The second diagram shows the losses that will occur.6 4 Ibid. 5 Ibid. 6 Ibid. ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010 Page 35 of 36 Section 4 – Testing Optical Fibre Cables Student Workbook 125 micron OD fibres with a 5 micron misalignment Section summary You should now understand how to use a power meter and an OTDR to test cables and diagnose faults. Further reading  Relevant operating manuals.  Search the internet using the term ‘fibre optics’. Section checklist You should now be able to:  test the power loss of a fibre cable with a optical power test  demonstrate the correct fibre optical characteristic trace as shown by an OTDR. Page 36 of 36 ICTCBL3013A Perform cable and system tests on customer premises © Commonwealth of Australia 2010