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9.4 Information systems: 2. Information can be transmitted in the form of waves
Syllabus reference (October 2002 version) |
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| 2. Electromagnetic radiation can be modulated to carry different types of information |
Students learn to: |
Students: |
Extract from Senior Science Stage 6 Syllabus (Amended October 2002). Board of Studies, NSW.
[Edit: 28 Aug 08]
Prior learning: Science Stages 4–
5 syllabus: Outcome 4.6 (content 4.6.4: sound energy), Outcome 5.6 (content
5.6.1: the wave model), Outcome 5.12 (content 5.12c:technology).
identify
the types of waves in the electromagnetic spectrum currently used for communication
systems as
– visible light
– infra-red
– microwaves
– radio waves, which include:
– TV
– FM radio waves
– AM radio waves
- There are several types of electromagnetic waves currently used in communication systems. These waves have a range of properties, making each type suitable for specific communication systems.
- The types of waves that are used for communication systems are:
- visible light, used in optical fibres
- infra-red, used as a laser beam and in thermal imaging
- microwaves, for satellite communication and radar
- radio waves, including AM radio band, FM radio band, and TV, which uses AM for the picture and FM for the sound.
Extra information on TV, radio
and satellite communication 
University of Texas, Austin, USA
perform a first-hand investigation to observe ways in which waves can be modulated to carry different types of information
- When performing the investigation, you
could modify a sound and observe the wave that it forms on a cathode ray oscilloscope
(CRO). Connect a microphone to the CRO and produce a sound by playing a note on an
instrument or using an audio oscillator. Change the frequency of the instrument by playing
a higher note or turning the dial on the audio oscillator and observing how the wave
changes. Try other variations of sounds, such as comparing the wave pattern produced by
the CRO from a wind instrument, a percussion instrument and a pipe organ.
- You could also use a signal generator and a cathode ray oscilloscope (CRO) to perform an examination of the effect on a wave of amplitude modulation (AM) and frequency modulation (FM).
compare the advantages and disadvantages of using microwaves and radio waves in communication technologies
- In general, the longer the wavelength, the more easily the waves
can penetrate built structures, water and the Earth. The first around-the-world
communication (short wave radio) used the ionosphere to reflect signals over the horizon.
Modern satellite based systems use very short wavelength signals, which include
microwaves.
Types of waves
Advantages
Disadvantages
Microwaves (very short wave length radio waves) Pass through the ionosphere, so are suitable for satellite to Earth transmission. Can be modified to carry many signals at one time, including data, television pictures and voice messages.
Absorbed very easily by natural, e.g. rain, and made objects, e.g. concrete. They are also absorbed by living tissue and may cause harm by their cooking effect. Need special aerials to receive them.
Radio waves Some are reflected off the ionosphere, so can travel around the Earth. Can carry a message instantaneously over a wide area.
Aerials to receive them are simpler than for microwaves.
The range of frequencies that can be accessed by existing technology is limited, so there is a lot of competition amongst companies for the use of the frequencies. Both microwaves and radio waves Wires are not needed as they travel through air, thus, a cheaper form of communication. Travel in a straight line, so repeater stations may be needed.
identify communication technologies that use energies from the electromagnetic spectrum for communication purposes
- The following table identifies some communication technologies that
use energies from the electromagnetic spectrum for communication purposes.
Communication
technologyDescription
Part of the electromagnetic spectrum used
Optical fibres Replacing copper cables in coaxial cables and phone lines as they last longer and carry 46 times more conversations than copper cables Visible light Remote control communication Remote controls for a variety of electrical devices, such as TV, video, garage doors and infra-red computer systems Infra-red Satellite technologies This technology mostly makes use of frequencies in the super high frequency (SHF) range and the extra high frequency (EHF) range. Microwaves Mobile phone networks These use a combination of systems. Electromagnetic radiation (EMR) is used to communicate between individual mobile phones and each local mobile exchange. Exchange networks communicate using land lines (coaxial or optic fibre). Microwaves TV broadcasting TV stations transmit in the very high frequency (VHF) range and the ultra high frequency (UHF) range. Shortwave radio; frequencies ranging from 1 Ghz – 150 Mhz. Radio broadcasting Radio is used for a broad range of technologies including AM and FM broadcasting and amateur radio. Radio dial indicated frequency range for FM: 88 – 108 megahertz.
Radio dial indicated frequency range for AM: 540 – 1600 kilohertz.
Shortwave and longwave radio; frequencies ranging from 10 Mhz – 1 Mhz.
More information about AM and FM radio and
TV , How Stuff Works.