This document discusses how digital signals are transmitted using electromagnetic waves. It explains that digital signals are strings of 1s and 0s representing sampled analogue signals. Electromagnetic waves emitted from a transmitter carry these digital signals by causing electrons in a receiver to vibrate, reproducing the original signal. Key characteristics of signals like amplitude, period, and frequency are defined. Frequency is calculated as the inverse of period and examples are given. A frequency spectrum shows the range of frequencies that make up a signal. Complex signals contain multiple frequencies combined.

1. Chapter 3 – Signalling with Electromagnetic Waves How Signals are Sent…

2. We know that analogue signals constantly change and digital signals have a value of 1 or 0.

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. 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

5. 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??

6. Electromagnetic Radiation From GCSE you should remember the EM Spectrum. An easy way to remember it is: Real Men Invariably Visit Ugly eX Girlfriends

8. 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.

9. 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…

10. Calculating Frequency Frequency = 1 / Period Calculate: Period, Amplitude and Frequency…

11. Calculating Frequency Frequency = 1 / Period Period = 20 ms Amplitude = 4V Frequency = 1/20ms = 50Hz

12. Calculating Frequency Frequency = 1 / Period Calculate: Period, Amplitude and Frequency…

13. Calculating Frequency Frequency = 1 / Period Period = 6.6 ms Amplitude = 4V Frequency = 1/6.6ms = 150Hz

14. Frequency Spectrum This shows the range of frequencies that a signal (waveform) contains. For example, the first waveform… Contains frequencies around 50Hz only

15. Frequency Spectrum The second waveform… Contains frequencies around 150Hz only

16. What about complex signals These contain a number of different frequencies on top of each other. Think of coloured light or the sound of an instrument. This is made up of several different frequencies – see how a wave can be made up…

17. Draw these waves onto graph paper. Draw the combined waveform.

18. Resulting Waveform