Chapter 3 – Signalling with Electromagnetic Waves How Signals are Sent…
We know that analogue signals constantly change and digital signals have a value of 1 or 0.
2 1 6 65536 16 … … … 2 9 512 9 2 8 256 8 2 7 128 7 2 6 64 6 2 5 32 5 2 4 16 4 2 3 8 3 2 2 4 2 2 1 2 1 2 n Number of Levels...
Redundancy <ul><li>To prevent errors in sending digital signals, more information is sent. </li></ul><ul><li>This can be s...
So how do we get digital signals? <ul><li>We use digital signals to send (or store) sampled analogue signals. </li></ul><u...
Electromagnetic Radiation <ul><li>From GCSE you should remember the EM Spectrum. </li></ul><ul><li>An easy way to remember...
 
What is a Signal <ul><li>Signals are emitted from VIBRATING MATTER. </li></ul><ul><li>These include sound waves, water wav...
Signal Properties <ul><li>A signal has several characteristics: </li></ul><ul><ul><li>Amplitude – the maximum displacement...
Calculating Frequency <ul><li>Frequency = 1 / Period </li></ul><ul><li>Calculate: Period, Amplitude and Frequency…  </li><...
Calculating Frequency <ul><li>Frequency = 1 / Period </li></ul><ul><li>Period = 20 ms </li></ul><ul><li>Amplitude = 4V </l...
Calculating Frequency <ul><li>Frequency = 1 / Period </li></ul><ul><li>Calculate: Period, Amplitude and Frequency…  </li><...
Calculating Frequency Frequency = 1 / Period Period = 6.6 ms Amplitude = 4V Frequency = 1/6.6ms = 150Hz
Frequency Spectrum <ul><li>This shows the range of frequencies that a signal (waveform) contains. </li></ul><ul><li>For ex...
Frequency Spectrum <ul><li>The second waveform… </li></ul>Contains frequencies around 150Hz only
What about complex signals <ul><li>These contain a number of different frequencies on top of each other. </li></ul><ul><li...
Draw these waves onto graph paper. Draw the combined waveform.
Resulting Waveform
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Chapter 3

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Chapter 3

  1. 1. Chapter 3 – Signalling with Electromagnetic Waves How Signals are Sent…
  2. 2. We know that analogue signals constantly change and digital signals have a value of 1 or 0.
  3. 3. 2 1 6 65536 16 … … … 2 9 512 9 2 8 256 8 2 7 128 7 2 6 64 6 2 5 32 5 2 4 16 4 2 3 8 3 2 2 4 2 2 1 2 1 2 n Number of Levels Number of Bits
  4. 4. Redundancy <ul><li>To prevent errors in sending digital signals, more information is sent. </li></ul><ul><li>This can be seen in a CD with a scratch or hole in it… </li></ul>Jarrow Sings the Blues MFI Records 1934
  5. 5. So how do we get digital signals? <ul><li>We use digital signals to send (or store) sampled analogue signals. </li></ul><ul><li>But is are a string of 1s or 0s sent???? </li></ul>Original Reconstructed 0110101100010101 How does this get sent??
  6. 6. Electromagnetic Radiation <ul><li>From GCSE you should remember the EM Spectrum. </li></ul><ul><li>An easy way to remember it is: </li></ul><ul><li>Real Men Invariably Visit Ugly eX Girlfriends </li></ul>
  7. 8. What is a Signal <ul><li>Signals are emitted from VIBRATING MATTER. </li></ul><ul><li>These include sound waves, water waves or electromagnetic waves. </li></ul><ul><li>Vibrating electrons in a transmitter emit radio waves. These are received by an aerial – the radio waves cause the electrons to vibrate producing a signal. </li></ul>
  8. 9. Signal Properties <ul><li>A signal has several characteristics: </li></ul><ul><ul><li>Amplitude – the maximum displacement </li></ul></ul><ul><ul><li>Period – time taken for 1 oscillation </li></ul></ul><ul><ul><li>Frequency – the number of oscillations per second </li></ul></ul><ul><ul><li>Frequency may not be limited to one – it can be made up of a range of different frequencies… </li></ul></ul>
  9. 10. Calculating Frequency <ul><li>Frequency = 1 / Period </li></ul><ul><li>Calculate: Period, Amplitude and Frequency… </li></ul>
  10. 11. Calculating Frequency <ul><li>Frequency = 1 / Period </li></ul><ul><li>Period = 20 ms </li></ul><ul><li>Amplitude = 4V </li></ul><ul><li>Frequency = 1/20ms = 50Hz </li></ul>
  11. 12. Calculating Frequency <ul><li>Frequency = 1 / Period </li></ul><ul><li>Calculate: Period, Amplitude and Frequency… </li></ul>
  12. 13. Calculating Frequency Frequency = 1 / Period Period = 6.6 ms Amplitude = 4V Frequency = 1/6.6ms = 150Hz
  13. 14. Frequency Spectrum <ul><li>This shows the range of frequencies that a signal (waveform) contains. </li></ul><ul><li>For example, the first waveform… </li></ul>Contains frequencies around 50Hz only
  14. 15. Frequency Spectrum <ul><li>The second waveform… </li></ul>Contains frequencies around 150Hz only
  15. 16. What about complex signals <ul><li>These contain a number of different frequencies on top of each other. </li></ul><ul><li>Think of coloured light or the sound of an instrument. </li></ul>This is made up of several different frequencies – see how a wave can be made up…
  16. 17. Draw these waves onto graph paper. Draw the combined waveform.
  17. 18. Resulting Waveform

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