Communication and signals. Book page Syllabus

Transcription

1 Communication and signals Book page Syllabus

2 What do these have to do with one another? Homer and the Internet

3 What are the codes they use?

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5 Do you know what changed WWII? The Imitation Game

6 Aim Know the difference between analogue and digital signals Describe how codes can be used to communicate Key words Communication Analogue signal Digital signal Modulation AM FM Noise

7 Have you ever wondered The bigger picture How has communication changed over time? A breif History of communication.mp4

8 Communicating using waves Talking to each other we use sound waves Communicating with a person further away we use light waves: - signaling with flags or beacons - radio and communication devices Telephone, fax machines, internet linked computers are used to transmit information To transmit the information, it must be converted into a stream of electrical pulses or light pulses These pulses can carry analogue or digital signals

9 Digital and analogue What is the difference between a digital signal and an analogue signal? What could they look like graphically? Digital signals can only be in one of two states, e.g. 0 or 1. This is called a binary code The code is converted into an electrical pulse Analogue signals are a continuously changing variable. The information is converted into electrical voltages or currents

10 Analogue signals A microphone converts sound waves into continuous electrical signals These signals are amplified and fed into a loudspeaker

11 Combination of digital and analogue Why is the analogue signal converted into a digital signal?

12 Noise All signals become weaker as they travel long distances, and they may also pick up random extra signals. This is called noise, and it is heard as crackles and hiss on radio programs. Noise may also cause an internet connection to drop or slow down, as the modem tries to compensate.

13 Noise Analogue Noise adds extra random information to analogue signals. Each time the signal is amplified, the noise is also amplified. Gradually, the signal becomes less and less like the original signal. Eventually, it may be impossible to make out the music in a radio broadcast against the background noise, for example.

14 Noise Digital Noise also adds extra random information to digital signals. However, this noise is usually lower in amplitude As a result, the electronics in the amplifiers can ignore the noise This means that the quality of the signal is maintained

15 Digital compared to Analogue ADVANTAGES Signals are clearer less susceptible to noise. Can be used quickly by computers. Carry digital signals using electromagnetic waves which travel at the speed of light. Carry much more information. Digital hardware is much smaller. Easier to send over long distances. DISADVANTAGES Digital hardware is more expensive Although digital signals are unaffected by electrical interference, they don t give a complete signal [just lots of samples] - some people feel that analogue vinyl records sound better than digital CDs for this reason. Which Which Noise What signal Examples is any is of noise? is most Electrical storms unwanted and are? Analogue Digital signal carries the most prone information? to noise? random information. thermal noise.

16 Communication systems Communication systems include the same basic components. You need to be able to define/describe the following: Encoder Modulator Transducer Amplifier Decoder Transmitter Receiver Storage

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18 Definitions Component Encoder Decoder Modulator Transmitter Receiver Storage Transducer Amplifier Function Changes information into readable form Changes information to original form Allows wave to carry impulses AM/FM Makes oscillations Collects information Stores information e.g. CD, DVD, tape Changes information into electrical form or the other way round (microphone, speaker) Increases intensity of received waves

19 AM and FM What do AM and FM stand for? AM amplitude modulation, where the sound wave is communicated by altering (modulating) the AMPLITUDE of the radio wave FM frequency modulation, where the sound wave is communicated by altering (modulating) the FREQUENCY of the radio wave More noise Easier to send How do they compare? AM FM Less noise Travels further Harder to send Travels shorter distances More noise Travels further Easier to send Less noise Travels shorter distances Harder to send

20 Question 1 Which of the following is not a use of total internal reflection? A. Periscopes B. Endoscopes C. Fibre optic communication D. Mirrors

21 Question 2 What does attenuation mean? A. Strengthening B. Increasing C. Larger D. Weakening

22 Question 3 One advantage of optical fibres over ordinary cables of the same thickness is: A B C they are made of glass they can carry more information their signals weaken more over long distances

23 Question 4 How do signals travel through optical fibres? A As microwaves B As radio waves C As infrared radiation or visible light

24 Question 5 What is a signal that varies continuously in frequency called? A B C A digital signal An analogue signal An AM signal

25 Question 6 How many different states are there in a digital signal? A B C One Two Three

26 Question 7 Which type of signal maintains a better quality? A Digital signal B Analogue signal C Both types are the same

27 Question 8 When a wave is made to carry a signal, the wave is said to be: A B C modified modulated diffracted

28 Question 9 Some signals are made of a series of pulses which are just off or on. These are called: A B C analogue signals digital signals wave signals

29 Question 10 Signals can pick up random additions on their way to the receiver, making the quality poorer. What word is used for these 'random additions'? A B C Dirt Noise Rubbish

30 Key words Communication exchange of information Analogue signal continuously varying electrical voltages or currents Digital signal information is converted into binary code, distinct electrical pulses Modulation - the process of varying one or more properties of a periodic waveform, usually either the amplitude or the frequency AM amplitude modulated wave FM frequency modulated wave Noise any unwanted information that distorts the original signal