UEE07 Electrotechnology Training Package UEENEEH046B Solve fundamental problems in electronic communications systems Learner Workbook Version 1 Training and Education Support Industry Skills Unit Meadowbank Product Code: 5173
Acknowledgments The TAFE NSW Training and Education Support Industry Skills Unit, Meadowbank would like to acknowledge the support and assistance of the following people in the production of this learner workbook: Writers: John Zervos Greg Denning Reviewers: Industry Skills Unit - Meadowbank TAFE NSW Project Manager: Steve Parkinson Industry Skills Unit - Meadowbank TAFE NSW Enquiries Enquiries about this and other publications can be made to: Training and Education Support Industry Skills Unit, Meadowbank Meadowbank TAFE Level 3, Building J, See Street, MEADOWBANK NSW 2114 Tel: 02-9942 3200 Fax: 02-9942 3257 The State of New South Wales, Department of Education and Training, TAFE NSW, Training and Education Support Industry Skills Unit, Meadowbank, 2010. Copyright of this material is reserved to TAFE NSW Training and Education Support Industry Skills Unit, Meadowbank. Reproduction or transmittal in whole or in part, other than for the purposes of private study or research, and subject to the provisions of the Copyright Act, is prohibited without the written authority of, TAFE NSW. Training and Education Support Industry Skills Unit, Meadowbank. ISBN 978-1-74236-196-3 Developed by Training & Education Support Industry Skills Unit, Meadowbank @ TAFE NSW 2010
Table of contents Introduction... 7 1. General introduction... 7 2. Using this learner workbook... 7 3. Prior knowledge and experience... 9 4. Unit of competency overview... 9 5. Assessment... 15 Section 1... 17 Introduction... 18 Section 2... 31 Skill Practice Section 2: The Yagi Antenna... 47 Section 3... 53 Skill Practice 3: Amplitude modulation... 68 Section 4... 76 Skill Practice Section 4: Frequency modulation in the time domain... 87 Section 5... 92 Skill Practice Section 5: Frequency modulation in the frequency domain... 99 Section 6... 102 Skill Practice Section 6: Tuned RF amplifiers... 108 Section 7... 114 Skill Practice Section 7: Measuring receiver selectivity... 127 Section 8... 134 Reference list... 180 Resource Evaluation Form... 182 Developed by Training & Education Support Industry Skills Unit, Meadowbank @ TAFE NSW 2010
Introduction 1. General introduction Welcome to UEENEEH046B Solve fundamental problems in electronic communication systems This national unit of competence is part of the UEE07 Electrotechnology Industry Training Package. 2. Using this learner workbook This learner workbook may be used on its own, or it may be used as additional material to support the development of knowledge and skills required to achieve this unit of competence. Group learning If you are studying this unit of competency as part of a group of learners your teacher will guide you in how to use these materials, including which learning topics and activities should be completed. Self-directing learning If you are studying this unit of competency as a self-directed learner you will have a facilitator assigned to you. This person will be available to support you as you work through this material. To study this unit effectively, learners who are working without facilitated group sessions should work through the materials in the order that they appear in the learner workbook, completing all the readings and all the activities. Learning strategies This learner workbook contains a variety of different learning activities to support the skills required to achieve this unit of competency. In addition to the activities described in this workbook, it is important that you discuss the issues raised with others such as your colleagues, friends, practitioners working in the field and other learners. Discussion plays an important role in understanding and remembering new information. To promote active learning: 1 Come up with your own answers first, before you attempt any readings 2 Compare and discuss your answers with others. 3 Research the topic and access readings, videos, etc. 4 Ask yourself, What do I think about the subject material now that I have studied it in depth? What have I learned? Page 7 of 183
Section 1 Requirements of a basic communications system In this section you ll develop a general understanding of basic communication systems, the need for modulation, and become familiar with the radio frequency spectrum. At the end of this section you should be able to: a) State the requirements of a basic communications system and list the main components. b) Define the terms simplex, half-duplex and full-duplex. c) List typical application of modern wired and wireless communications systems. d) Explain the meaning of the term Baseband signal and list three signal types. e) Draw the baseband signal in both the time and frequency domains. f) Explain the need for modulation in communication systems g) State the various forms of modulation method used in modern communication systems h) Explain the relationship between the frequency of the baseband signal and the bandwidth requirements of the transmitter. i) List the radio frequency spectrum of VLF through to EHF. j) State the frequency bands used by AM commercial broadcasting, FM commercial broadcasting and analogue and digital television. k) State the hazards associated with working with radio transmitters and antennas and describe the necessary control measures. Page 17 of 183
Summary of technical information Introduction The purpose of any communication system is to convey information from a source to a destination. For example, in human conversation, a message is normally conveyed from the speaker (source) to the listener (destination). This purpose is also true for an electronic communications system. The main difference being that in a (wireless) electronic communications system, electromagnetic waves are used to transmit and receive the information. The information signal is referred to as either the message, baseband, or intelligence signal. Simplex electronic communication systems only allow for information to be sent in one direction only, such as in commercial radio and television broadcasts. Half-duplex systems allow communication in both directions but not at the same time (e.g. CB radio), while full-duplex systems allow communication in both directions simultaneously (e.g. telephone). Electronic communications systems may be wired or unwired. Examples of wired communications systems include cable television, telephony and computer network systems. Examples of wireless communications include mobile telephone, commercial AM and FM broadcasts, regular and satellite television, two-way radio, wireless computer networks, and Bluetooth. (Bluetooth is a wireless technology for exchanging data over short distances from fixed and mobile devices, creating Personal Area Networks.) There is little doubt that electronic communications is integrated into all areas of the electronics industry, including the computing and electronic security industries. Therefore, even if you do not choose to specialise in the area of electronic communications, a basic understanding of electronic communications principles is critical to your role as an electronic technician or engineer. The basic block diagram of an electronic communications system All electronic communications systems can be represented by a common block diagram consisting of a source, transmitter, medium, receiver, and destination, as shown in Figure 1. Noise Source Transmitter Medium Receiver Destination Figure 1: The basic block diagram of an electronic communications system The source is the intelligence, baseband, or message signal that contains the information to be transmitted (typically voice, music, video, and data). Page 18 of 183
The transmitter contains the necessary circuitry for converting the intelligence signal into a form capable of being propagated (transmitted) over the medium. Normally, this will entail placing the intelligence signal on a higher frequency carrier signal through a process called modulation. Modulation methods that you may already be familiar with include amplitude modulation (AM) and frequency modulation (FM). The medium is the environment over which the signal is transmitted, which will normally be copper cable, fibre optic cable, or the atmosphere (in the case of wireless communications). The medium can be divided into a number of separate channels to accommodate more than one intelligence signal. (The international commission CCIT [renamed ITU-T] defines a channel as a single one way path for the transmission of electric signals.) Multiple channels are achieved by assigning a different carrier frequency to each channel. The receiver accepts the transmitted signal and demodulates it (if it was modulated in the transmitter) to recover the original intelligence signal. The destination is the where the recovered intelligence signal ends up. This could be a loudspeaker, video screen, computer, or the audio/video/data inputs of some other component. Noise Electrical noise is defined as any unwanted signal that is superimposed on the desired signal. While noise can enter the system at any point, the medium is the most vulnerable because the signal is usually at its weakest and most susceptible to outside influence. Activity 1 - Noise 1. What does radio noise sound like? 2. Think about AM and FM radio broadcasts that you have listened to. Which do you recall as being inherently less noisy? 3. What does noise look like on a video screen? Page 19 of 183
A relative measure of the amount of noise in a system is given by its signal to noise ratio (SNR), which is the ratio of desired signal power to noise power expressed in decibels. That is: P SNR = 10 log 10 P Signal Noise Where: SNR = Signal-to-noise ratio (db) Need for modulation P Signal = Signal power (W) P Noise = Noise Power (W) Baseband signals, such as voice and video, are not directly suited for radio transmission. This is because they have a relatively low frequency which, as you will see in the next section, means they have a poor radiation efficiency and would require very long transmit and receive antennas; possibly in the order of kilometres long! For these reasons, the baseband signal is normally modulated (encoded) onto a higher frequency carrier waveform. The higher frequency carrier waveform can be transmitted more efficiently, and requires smaller transmit and receive antenna lengths. When you tune into a radio or TV station, you are actually tuning in to its carrier frequency! Types of modulation method There are many types of modulation method used in electronic communications. Some of the more common ones are briefly described below, with fuller treatment given throughout the remainder of this workbook. Amplitude Modulation (AM) The amplitude of a high frequency sine wave carrier is modulated (varied) in accordance with the instantaneous amplitude of the baseband signal. Full AM is referred to as Double Sideband Full Carrier (DSBFC) AM. Variations of this are Single Sideband Suppressed Carrier (SSBSC) and Vestigial Sideband (VSB). Frequency Modulation (FM) The frequency of a high frequency sine wave carrier is modulated (varied) in accordance with the instantaneous amplitude of the baseband signal. Page 20 of 183
Phase Modulation (PM) The phase of a high frequency sine wave carrier is modulated (varied) in accordance with the instantaneous amplitude of the baseband signal. Phase modulation is similar in many ways to frequency modulation. Quadrature Amplitude Modulation (QAM) This is a combination of phase and amplitude modulation. The radio frequency spectrum The range of frequencies used in radio communications is referred to as the radio frequency spectrum. Different parts of this spectrum are used for different radio transmission technologies and applications. Each technology or broadcast station is assigned a frequency by the Australian Communications and Media Authority. The assigned frequency or channel will be in a section of the radio spectrum that has been set aside for that particular type of communication or broadcast service. The radio frequency spectrum is broken up into groups for ease of identification, as summarised in Table 1. Abbreviation Name Bandwidth VLF Very Low Frequency 3 khz to 30 khz LF Low Frequency 30 khz to 300 khz MF Medium Frequency 300 khz to 3000 khz HF High Frequency 3 MHz to 30 MHz VHF Very High Frequency 30 MHz to 300 MH UHF Ultra High Frequency 300 MHz to 3000 MHz SHF Super High Frequency 3 GHz to 30 GHz EHF Extra High Frequency 30 GHz to 300 GHz Table 1: Division of the radio frequency spectrum Page 21 of 183