DIGITAL VS ANALOGUE LEARNING TARGET I CAN... DESCRIBE THE DIFFERENCE BETWEEN ANALOGUE AND DIGITAL SIGNALS TO EXPLAIN THE ADVANTAGES AND DISADVANTAGES OF USING EACH SIGNAL. WHAT TYPE(S) OF ELECTROMAGNETIC WAVES ARE USED FOR COMMUNICATION? • THE RADIO AND MICROWAVE SPECTRUM IS DIVIDED INTO FREQUENCY BANDS. • THE HIGHER THE FREQUENCY OF THE WAVE: • THE MORE INFORMATION THEY CARRY. • THE SHORTER THEIR RANGE • THE LESS THEY SPREAD OUT (DIFFRACT) Waveband Frequency range Use Microwave +3000 MHz Satellite TV, phones UHF (ultra-high frequency) 300-3000 MHz Terrestrial TV, Mobile phones VHF (very high frequency) 30-300 MHz Local Radio, emergency services MF (medium frequency) 300 kHz – 3 MHz National Radio (analogue) LF (low frequency) Less than 300 MHz International Radio (analogue) Radio waves are not absorbed strongly by walls, which is why radio (and television) signals can be received indoors. Tall objects, like buildings and hills, can prevent radio waves travelling directly from a transmitter, but this is not always a problem. In some areas, the reflection of waves off other buildings or hills can actually lead to improved radio reception. Low frequency (up to 3 MHz) radio waves travel along the Earth’s surface and can travel hundreds of miles. These ground waves are used for local and national radio. Higher frequency radio waves (3–30 MHz) are reflected off the ionosphere high in the atmosphere. These sky waves are used for international and amateur radio. The ionosphere is stronger in the summer than winter so you can listen to radio stations from a greater distance. Microwaves are very high frequency radio waves (over 30 MHz). Unlike other radio waves, they are not reflected by the ionosphere but pass straight through and into space. This means that they can be picked up by satellites and transmitted over very large distances right round the Earth. In your own words answer these on your guided notes: 1. Describe the difference between using radio waves and microwaves for communication. 2. Explain how the ionosphere is used for communication. Draw a diagram to support your explanation. Think about other methods of sending a signal between two locations. Optical fibers are increasingly being used for communications instead of traditional copper wires. Optical fibers have a number advantages over copper wires: They are cheaper. They are thinner and lighter. Signals can travel further. Not affected by electromagnetic signals so no interference. Several digital signals can be carried by one fiber. Signals do not weaken as much while they travel. More secure – they are almost impossible to bug. An Analogue Wave: Amplitude varies continuously Frequency varies continuously It can have any value within a range. Where used: Dimmer switches, thermometers, speedometers and old-fashioned watches. These are coded pulses. Only made up of two values – 1 ‘on, or 2 ‘off’. Where used: On/off switches, digital clocks and meters. current An Digital Wave: time In your own words answer these on your guided notes: 1. Describe the difference between an analogue and digital signal. 2. Describe the advantages of using a digital signal over an analogue signal.