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Descrição
FlashCards por James Middleton4075, atualizado more than 1 year ago
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Criado por James Middleton4075
mais de 9 anos atrás
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| Questão | Responda |
| What type of waves are used to communicate with satellites in a low polar orbit and what type are used for waves with a high geostationary orbit? | Low frequency radio waves are used for low orbit satellites and higher frequency radio waves are used for geostationary satellites. |
| Describe two features of a radio wave | They have a low frequency and very long wavelength. |
| Radio waves with a frequency below what MHz are reflected by the ionosphere? | 30MHz |
| Radio waves with a frequency above what GHz are reduced in strength because they are absorbed and scattered by rain, dust and other effects in the atmosphere? | 30GHz |
| Radio waves between what frequencies can pass through the Earth's atmosphere/ | 30MHz and 30GHz |
| What type of signals are used in satellite communication and why? | Digital signals are used because they are less likely to suffer from interference than analogue signals. |
| What other type of waves are used to transmit information to satellites? | Microwaves - they have a shorter wavelength and higher frequency than radio waves. |
| Why does the dish used in satellite communication have to be many times larger than the wavelength when using microwaves? | So that the waves are captured and focus onto the receiver. Microwaves have a very short wavelength which means they are not likely to be diffracted so the beam remains narrow and focused. This is why also the transmitter and receiver have to be well aligned. |
| How is diffraction useful? | It is useful because it means that radio waves can get around obstacles. So if there is a hill in the way then it will not affect the signal. |
| What are the types of diffraction and what they look like? | pg78 for diagrams and types |
| The amount that a wave is diffracted by depends on the size of the gap and the wavelength of the wave. What do large gaps do and when does maximum diffraction happen? | Large gaps simply allow the wave to pass straight through without diffracting much. Maximum diffraction happens when the size of the gap is equal to the wavelength. |
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