Radio Refraction and Interferance
- Wireless technology is used by:
- radio and television
- mobile phones
- Radio waves are reflected and refracted in the Earth's atmosphere:
- The amount of refraction depends on the frequency of the wave.
- There is less refraction at higher frequencies.
- Radio stations broadcast signas with a particular frequency.
- The same frequency can be used by more than one radio station:
- The radio stations are too far away from each other to interfere.
- But in unusual weather conditions, the radio waves can travel futher, and the radio waves can interfere.
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Radio Refraction and Interferance 2
Interferance is reduced if digital signals are used.
- Digital Audio Broadcasting (DAB) also provides a greater choice of radio stations but the audio quatlity isn't as good as the FM signals currently used.
- DAB eliminates interferance between other radio stations.
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- Radio waves are reflected from ionosphere. They behave like light in an optical fibre and undergo total internal reflection.
- Ionosphere- a region of the Earth's atmosphere where ionisation caused by incoming solar affects the transmission of radio waves; it extends from 70km to 400km above the Earth's surface.
- Ionisation- The formulation of ions (charged particles).
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Radio Refection 2
- Water reflects radio waves but land mass does not.
- Continued reflection by the ionosphere and the oceans allow radio waves to be recieved from an aerial that is not the line of sight.
- Microwaves pass through the ionosphere.
- Microwave signals are recieved by orbiting satellites, amplified and retransmitting back to Earth.
- Communication satellites orbit above the equatorand take 24 hours to orbit Earth.
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- Radio waves are diffracted when they meet an obstruction.
- Refraction in the atmosphere needs to be taken into account when sending a signal to a satellite.
- The transmitting aerial needs to send a focused beam to the satellite because its aerial is very small.
- The transmitted beam is slightly divergant.
- Some energy is lost from the edge of the transmitting aerial becuse of diffraction.
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