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Cambridge TECHNICALS OCR LEVEL 2 CAMBRIDGE TECHNICAL CERTIFICATE/DIPLOMA IN SCIENCE SCIENCE OF TELECOMMUNICATIONS Y/505/3127 LEVEL 2 UNIT 15 GUIDED LEARNING HOURS: 60 UNIT CREDIT VALUE: 10 SCIENCE OF TELECOMMUNICATIONS Y/505/3127 LEVEL 2 AIM AND PURPOSE OF THE UNIT This unit will allow learners to understand that communication is a vital part of modern society. We gather information from the internet, television and radio. We use telephones, e-mail, mobile phones, pagers, faxes, navigational systems and video conferencing to communicate with each other. Communication systems are used to carry information such as: • pictures, both still and video • sound, such as music and voices • computer data (bits) Information is carried in a variety of ways including through free space, through optical fibres and as electricity through metal wires. Although information being transmitted may be blocked by obstacles there are ways to overcome these obstacles. This unit aims to address these areas so learners have a thorough understanding of current communication systems. www.ocr.org.uk 2 Science of Telecommunications Level 2 Unit 15 ASSESSMENT AND GRADING CRITERIA Learning Outcome (LO) Pass Merit Distinction The assessment criteria are the pass requirements for this unit. To achieve a merit the evidence must show that, in addition to the pass criteria, the learner is able to: To achieve a distinction the evidence must show that, in addition to the pass and merit criteria, the learner is able to: D1 describe the factors that influence the choice of a communication system The learner will: The learner can: 1 Know how current telecommunication systems can be used to communicate information. P1 describe the different types of communication systems we use every day M1 evaluate the advantages and disadvantages of each type of system 2 Know the properties of waves. P2 identify the general properties of waves M2 describe the properties of waves 3 Know how electromagnetic waves can be used in communication. P3 describe how the different types of electromagnetic waves are used in different communication systems M3 explain the advantages and disadvantages in using electromagnetic waves for communication D2 explain why the different types of electromagnetic waves are used in different communication systems 4 Know some of the problems in transmitting messages. P4 describe the impact of specific obstacles on transmitted messages M4 compare the level of impact of obstacles on transmission D3 explain how obstacles to transmission can be overcome 3 TEACHING CONTENT The unit content describes what has to be taught to ensure that learners are able to access the highest grade. Anything which follows an i.e. details what must be taught as part of that area of content. Anything which follows an e.g. is illustrative, it should be noted that where e.g. is used, learners must know and be able to apply relevant examples to their work though these do not need to be the same ones specified in the unit content. LO1 Know how current telecommunication systems can be used to communicate information. LO2 Know the properties of waves. Current types of communication systems • Waves through free space, used for: -- Radio broadcasting -- TV broadcasting -- Mobile phones -- Pagers -- Visible light communication (e.g. Traffic lights, warning lights) -- Infra-red communication (e.g. remote control, night viewing) • Transverse waves • Longitudinal waves -- Wavelength (λ) - the distance between two successive peaks or troughs and is measured in metres, m -- Amplitude - the measure of the energy carried by a wave -- Frequency (f) - the number of complete wave cycles per second and is measured in Hertz (Hz). -- Reflection • Light waves travel in straight lines but are reflected by a mirror -- Be able to label and calculate the angle of incidence (angle of the light hitting the mirror) equals the angle of reflection (angle of light leaving the mirror) -- Refraction • If light waves pass across the boundary between two substances with different densities, the speed of the light waves changes and causes a change of direction. If light passes from air to glass it slows down, as glass is denser than air. The angle of bend can be measured by passing a light beam at an angle into a glass block and measuring the angle as the beam is bent in the glass block. • The refractive index - a measure of how much the light is slowed down and therefore bent. The more dense the substance, the more the light is slowed down and bent, and the higher the refractive index. The refractive index can be calculated using the equation (Snell’s Law): General properties of waves: • Optical fibre, used for: -- Cable TV networks -- Telephone networks -- Computer networks • Copper cable (also coaxial cable), used for: -- Telephone conversation network -- Analogue TV Considerations when using communication systems • Signal considerations: -- Bandwidth – a large bandwidth will increase the rate of data transfer. Copper wire has a small bandwidth but optical fibre has large bandwidth -- Distance – signal intensity will decrease with distance -- Attenuation – fading of a signal and can result from the combined effect of scattering (reflection in other directions than signal direction) and absorption (wave energy is converted to other forms of energy). For example visible light is easily absorbed and scattered by fog, rain, smoke and air -- Interference – when waves meet they can create interference which can either be constructive interference (resulting in summation of wave amplitude) or destructive interference (resulting in subtraction of wave amplitude) sin i (angle of incidence) sin r (angle of refraction) -- Diffraction • Diffraction is the spreading out of a wave as it passes an obstacle or gap. Diffraction occurs if the gap or obstacle is the same size or smaller than the wave. The diffraction of water waves is easily seen in a ripple tank. Light diffracts, but the gap causing it needs to be very small as its wavelength is very short being measured in nanometers (nm). • Equipment considerations: -- Portability -- Cost -- Maintenance www.ocr.org.uk Refractive index = Speed of light in air Speed of light in substance 4 Science of Telecommunications Level 2 Unit 15 • Diffraction of light can be seen by passing a light radio transmitter to the receiver. Interference occurs if two beam through diffraction gratings which have radio stations transmit on the same frequency, leading to at least 100 lines per mm. As light is made up of regulation of the parts of the electromagnetic spectrum colours of different wavelengths it may give the by authorities. One of the other main problems to be effect as shown around a candle. overcome with radio waves is the curvature of the Earth. • Some radio waves diffract around hills or into • Long waves (100 km – 1 km) tunnels giving a weaker signal. Long wave radio waves diffract (bend) along the Earth’s -- Interference surface, allowing transmission across long distances. • Interference occurs when two or more waves They also diffract over mountains and into buildings and overlap. If two crests of a wave are superimposed tunnels. Used for AM radio (on top of each other) then the two waves become • Medium waves (1 km – 100 m) one bigger wave. This is constructive interference. Medium wave radio signals bounce off part of the Earth’s But if the waves are out of phase, a crest overlaps a atmosphere called the ionosphere. They can travel long trough then the wave is reduced. This is destructive distances around the Earth, but the signal is often poor interference. This can be demonstrated on an due to interference. Was used for BBC 5 oscilloscope with two signals. • Short waves (100 m – 10 m) Short wave radio waves are used to transmit TV and FM radio. The signal is sent from the transmitter on the Earth’s surface to a geostationary satellite which is placed at the same position above the Earth. The satellite reflects the signal to the receiver on a different part of the Earth’s surface. Short wave radio can only be sent if the satellite is in ‘view’ of both the transmitter and receiver, so it cannot be sent around the Earth in one go. The signal is however high quality and sharp. This type of radio wave will not diffract over hills or far through buildings. Also included are: VHF (10 m – 1 m) used by taxis UHF (1 m – 10 cm) used by police radio • Total internal reflection -- If the angle a wave enters a new medium is too great, the wave cannot pass through it, but is reflected back. -- The critical angle of a substance is the angle of incidence in the less dense medium at which the ray just manages to escape the denser medium. If the angle of incidence is greater than the critical angle, total internal reflection occurs. This is when the incident ray cannot escape through the substance and is totally reflected. -- Total internal reflection only happens if: • The angle of incidence is greater than the critical angle for a substance. • The rays are travelling in a denser medium, such as glass, to a less dense medium, such as air. • Light waves -- Visible light (10µm – 1 µm) is used in a wide range of applications, from traffic lights to warning beacons. LO3 Know how electromagnetic waves can be used in communication. Parts of the electromagnetic spectrum used in communication • Infra-red waves (100 µm – 10 µm) -- Infra-red is also part of the electromagnetic spectrum and used in remote controls, however, as it has a very short wavelength compared with radio waves, it is easily absorbed and scattered by the atmosphere. • Micro-waves (10 cm – 100 µm) Microwaves are used for mobile phone communication. They cannot be broadcast like radio waves, so the receiver needs to be in the line of sight of the transmitter. The transmitter and receiver need to be very high (e.g. on top of the BT tower) to reduce buildings, hills or the Earth’s curvature blocking the rays. In the UK there are 200 microwave stations each about 50 km apart to account for the Earth’s curvature. Factors that affect the use of electromagnetic waves in communication, e.g. • Fog • Cloud • Solid obstacles • Curvature of the Earth • Radio waves Radio waves easily pass through clouds and fog and can be sent long distances through the atmosphere from the • Distance • Line of sight 5 • Diffraction • Absorption LO4 Know some of the problems in transmitting messages. • Factors that affect transmissions -- Attenuation -- Bandwidth -- Bulky repeater station -- Moving transmission -- Cost -- Health risk -- Environmental impact -- Interference -- Security Transmission problem -- Partial blocking the beam -- Blocking the beam -- Beam wander -- Interference -- Distance • Obstacles to transmission -- Solid obstacles - buildings, walls, trees, hills, dust -- Climate – heat, fog, mist, rain, wind -- Vibration – noise, physical shaking -- Light -- Transmissions The impact of each of these obstacles should be considered. • Reducing obstacles to transmission -- Increase beam width -- Reflectors -- Focusing dishes -- Insulation surroundings -- Delivery guidance www.ocr.org.uk 6 Science of Telecommunications Level 2 Unit 15 DELIVERY GUIDANCE LO1 Know how current telecommunication systems can be used to communicate information. • Addition – two waves can produce a single complex wave by sounding two different tuning forks into the microphone. Learners may start the unit by composing a diary of the telecommunications that they use day to day. This could lead onto a discussion about the widespread use of telecommunications and why it is important to them and the development of a country. Light waves can be used to demonstrate: • Reflection • Refraction The discussion could be approached from the importance of telecommunications in the World’s economy which is underlined by the fact that in 2012 the global telecommunications industry generated about a £2.96 trillion. • Total Internal Reflection Learners could research the different types of communication systems we use every day. Learners could produce a table comparing the advantages and disadvantages of different communication systems. Total internal reflection can be demonstrated by passing a beam of light into a semi-circular prism at various angles. This learning outcome gives learners the opportunity to carry out a number of short practical investigations; these investigations could be undertaken in a ‘blacked out’ room with blinds shutting out light from windows. The use of lasers, micro-waves or infra-red beams could also be used if available. Learners should investigate: wavelength, amplitude, frequency, reflection, refraction, diffraction, interference and total internal reflection. Learners will summarise the parts of the electromagnetic spectrum including radio waves, visible light and infra-red used in communication. This learning outcome can be linked to LO1. • Diffraction • Interference Learners are expected to produce notes from their practical investigations in a course note book. It should be noted the In discussion, groups could consider the factors that influence presentation of the notes should allow for a moderator to understand the procedures and outcomes undertaken by the customer choice when choosing a communication system. learner. This learning outcome can be linked to LO3. LO3 Know how electromagnetic waves can be used in communication. LO2 Know the properties of waves. Learners are required to produce a description of the types of electromagnetic waves that are used in communication systems and to explain their advantages and disadvantages when used for communication. This learning outcome could be introduced by showing the learners how light waves travel by using a ripple tank. Learners would be expected to produce a comparison table of wavelength against the advantages and disadvantages when used for specific communication applications. This could be in the form of an informative leaflet. An oscilloscope will give a visual display of wave properties. This can be done by connecting a microphone to the oscilloscope and by using sound. It can be used to demonstrate: LO4 Know some of the problems in transmitting messages. This learning outcome may be more interesting if learners had the opportunity to investigate the problems and solutions in a practical setting. If light waves or micro-waves are used in the classroom, obstacles could be introduced and using ideas from LO2 learners could provide solutions; this in turn would reinforce learning in LO4. • Wavelength – a long wave will have a low frequency (or low pitch) where as a short wave will have a high frequency (high pitch). • Amplitude – a loud sound will have a large amplitude as the wave contains more energy. In any communication system, some of the signal is absorbed by the material it travels in. This can be demonstrated by a beam of visible light or infra-red shown through smoke, • Quality – the waveform of a sound will show its tone, a smooth waveform can be produced by a tuning fork. 7 representing fog, rain or smoke in the air, in a smoke-box it will be absorbed and scattered by the smoke. This fading of the signal is called attenuation. If a light wave or infra-red wave is to be transmitted through the air, it is possible that things can get between the transmitter and receiver and reduce the size of the signal or block it altogether. Such problems could be caused by birds, fog, rain or sandstorms (this is known as noise). The beam of light in an optical fibre will also become weaker the further it travels. In addition, waves from other sources (both light and infra-red) can find their way into the receiver. Another serious problem is caused by vibration from traffic or wind that can shake the transmitter and cause the transmitted beam to ‘wander’. This can be demonstrated by placing obstacles in the path of a beam of light; moving the receiver further away from the transmitter; allowing more light into the room; shaking the transmitter. In the laboratory, learners could transmit a signal, which could be a beam of light, to be received by a light sensor and investigating how to overcome obstacles placed in the path of the signal to produce the optimum received transmission. Possible obstacles:Transmission problem Obstacles to transmission Partial blocking the beam. Smoke to represent: Birds, fog, rain, mist, dust, sandstorms Blocking the beam Solid blocks to represent: Buildings, trees, hills Reducing obstacles Increase beam width but this may reduce beam intensity. Use reflectors to pass beam around obstacles. Vibration (beam wander) Traffic vibration, wind Increase beam width but this may reduce light intensity. Waves from other sources Light from other sources and surroundings Increase beam intensity by use of focusing dish. Receiving dish focusing the beam. Card tube around receiving LDR cuts out a lot of background light. Distance Position of transmitter and receiver Increase beam intensity. Use of light pipe or optical fibres to guide light signal over longer distances. • Learners would be expected to produce notes from their practical investigations in a course note book. www.ocr.org.uk 8 Science of Telecommunications Level 2 Unit 15 SUGGESTED ASSESSMENT SCENARIOS AND GUIDANCE ON ASSESSMENT Criteria L01 Assignment title ‘Which Report’ into telecommunication companies Scenario Assessments Learners research telecommunication companies and suggest which ones present the best system for customers. Learners, themselves, may carry out surveys into customer appreciation of telecommunication companies. Learners produce a comparison table of current telecommunication systems. P1 Learners will state what the systems are and a description of how the system is used in communication. M1 Learners need to demonstrate the advantages and disadvantages of the systems for customers. Quantitative data may be used when comparing bandwidth and quality but in terms of maintenance and cost data may well be ‘hear say’ based on reported customer surveys. D1 Factors that affect choice of communication are included in the table. L02 Wave properties – practical investigations Learners investigate the properties of waves covering the listed content. P2 Learners produce notes in a note book which outlines the properties of waves used in communication. M2 Learners will need to describe these properties in some detail. L03 Logistics for war communications Fitting out an army will require a range of communication systems. Controlling drones or communicating with and within a scouting party will require different communications based on different wavelengths. A modern warship or aeroplane will use a range of communication wavelengths when detecting objects or when talking to people around the globe. Learners should consider the appropriate wavelength for the appropriate communication factors involved and produce a “handy leaflet” directing personnel to the appropriate wavelength. 9 P3 Learners need to produce a leaflet that lists the appropriate electromagnetic waves needed to be used for particular scenarios. M3 Learners need to expand on their descriptions giving the advantages and disadvantages for the wavelength that is being used. They should consider which wavelength might be suitable for global communication or for short distances when large amounts of data need to be transmitted. D2 Learners need to describe in some detail why a certain wavelength is used in particular communication situations. Criteria L04 Assignment title Improving transmission Scenario Assessments Learners are set a particular problem that interferes with transmitting a signal. They need to produce the best solution to the problem. P4 Learners produce notes in a note book, identifies the obstacles, leading to a description of their impact on the transmission signal. M4 Learners compare the level of impact on transmission giving the optimum reception of the signal. D3 It is expected that the solution is treated in terms of quantitative measurements. www.ocr.org.uk 10 CONTACT US Staff at the OCR Customer Contact Centre are available to take your call between 8am and 5.30pm, Monday to Friday. We’re always delighted to answer questions and give advice. Telephone 02476 851509 Email [email protected] www.ocr.org.uk