Like this presentation? Why not share!

# Chapter 3

## by PhysicsJackson on Jan 31, 2008

• 371 views

### Views

Total Views
371
Views on SlideShare
371
Embed Views
0

Likes
0
0
0

No embeds

### Categories

Uploaded via SlideShare as Microsoft PowerPoint

## Chapter 3Presentation Transcript

• 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 Number of Bits
• Redundancy
• To prevent errors in sending digital signals, more information is sent.
• This can be seen in a CD with a scratch or hole in it…
Jarrow Sings the Blues MFI Records 1934
• So how do we get digital signals?
• We use digital signals to send (or store) sampled analogue signals.
• But is are a string of 1s or 0s sent????
Original Reconstructed 0110101100010101 How does this get sent??
• From GCSE you should remember the EM Spectrum.
• An easy way to remember it is:
• Real Men Invariably Visit Ugly eX Girlfriends
•
• What is a Signal
• Signals are emitted from VIBRATING MATTER.
• These include sound waves, water waves or electromagnetic waves.
• 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.
• Signal Properties
• A signal has several characteristics:
• Amplitude – the maximum displacement
• Period – time taken for 1 oscillation
• Frequency – the number of oscillations per second
• Frequency may not be limited to one – it can be made up of a range of different frequencies…
• Calculating Frequency
• Frequency = 1 / Period
• Calculate: Period, Amplitude and Frequency…
• Calculating Frequency
• Frequency = 1 / Period
• Period = 20 ms
• Amplitude = 4V
• Frequency = 1/20ms = 50Hz
• Calculating Frequency
• Frequency = 1 / Period
• Calculate: Period, Amplitude and Frequency…
• Calculating Frequency Frequency = 1 / Period Period = 6.6 ms Amplitude = 4V Frequency = 1/6.6ms = 150Hz
• Frequency Spectrum
• This shows the range of frequencies that a signal (waveform) contains.
• For example, the first waveform…
Contains frequencies around 50Hz only
• Frequency Spectrum
• The second waveform…
Contains frequencies around 150Hz only