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2. Wireless Transmission 25 Our topic is still about sending data But this time we’re looking at ways that don’t use any cables We all use wireless transmission every day We’ll look at three familiar technologies But you need to know a little bit about how they work And you need to know why each technology is used in different ways in your everyday life…

3. Wireless Transmission 25 Infrared Satellite Microwave Short Range Medium Range Long Range

4. Wireless Transmission 25 So you’re only expected to know about those three wireless technologies But to understand even a bit about how they work, it’s worth spending a couple of minutes on some background You won’t need this for the exam But it should help you understand the basics a bit better…

5. Wireless Transmission 25 Backgrounder – Waves In Science, you learn about waves, wavelength and amplitude You also know about frequency based on different wavelengths High Frequency Low Frequency Wavelength Amplitude Hz = Hertz Cycles per second

6. Wireless Transmission 25 Backgrounder – Spectrum From Science, you also know about the electromagnetic spectrum This is energy travels in waves and spans a spectrum from very long radio waves to very short gamma rays. Our eyes eye can only detect a small ‘visible light’ part of this spectrum And we primarily use the middle of the spectrum for communication So when you send a text message, or watch TV or tune a radio, you are using electromagnetic energy Without these wireless waves, the world you know could not exist.

7. Wireless Transmission 25 Backgrounder – Cables & Digital Data Here’s the part of the EMS used for communication Kilo = Thousands of cycles per second Mega = Millions of cycles per second Giga = Billions of cycles per second

8. Wireless Transmission 25 Backgrounder – Radio Waves & Digital Data Radio waves have the longest wavelengths, from 30cm to several miles long. Radio waves are often used to transmit data and have all sorts of applications including radio, satellites, radar, and computer networks. Microwaves are shorter than radio waves with wavelengths measured in centimeters. We use microwaves to cook food as well as to transmit information Microwaves are useful in communication as they can penetrate clouds, smoke, and light rain

9. Wireless Transmission 25 Backgrounder – Radio Waves & Digital Data So, how do these waves actually carry data? The answer is modulation, which means changing a wave by the signal we transmit You know this from radio, where modulation is done by amplitude (AM) or frequency (FM)

10. Wireless Transmission 25 Backgrounder – Radio Waves & Digital Data So for digital data, you transmit 1s & 0s by modulating a wave by frequency or amplitude Send 1s at a low frequency and 0s at a high frequency Send 1s at a high amplitude and 0s at a low amplitude 10010 10010

11. Wireless Transmission 25 Infrared Satellite Microwave Short Range Medium Range Long Range

12. Wireless Transmission 25 Infrared Uses infrared light to transmit data That’s very high frequency light It’s a reliable method used for TV remotes & keyboards etc But only works in short range And devices must be in line of sight Can also suffer from interference

13. Wireless Transmission 25 Microwave Uses waves with short wavelengths to transmit data That’s microwaves Good for medium distances (‘Personal Area Network’ or PAN) Examples are Bluetooth devices, such as headsets or keyboard & mice Can suffer from interference from other devices eg a microwave oven that’s near to a computer device on same frequency

14. Wireless Transmission 25 Satellite Uses satellites in space to relay data between points on earth Examples include GPS or satellite TV Good for very long distances But expensive

15. Wireless Transmission 25 Infrared Satellite Microwave Short Range Medium Range Long Range

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17. Wireless Transmission 25 Devices using wireless networking need a NIC Network Interface Card It’s the hardware for receiving wireless signals It’s built-into modern devices eg tablets & phones The NIC connects to a NAP Network Access Point Lots of places offer NAPs, such as cafes & libraries. Wireless networking is great – but always remember that you can only connect to the Internet if you have a signal!

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