Download science

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