wireless communications- radio waves...
- Created by: chelsea todd
- Created on: 12-01-16 17:05
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- wireless communications- radio waves...
- long wavelengths travel well through earth atmosphere...
- radio waves and microwaves are good at transferring information over long distances
- this is because they dont get absorbed by the earths atmosphere as much.
- uses of radio waves
- radio waves are used for broadcasting radio and tv programmes
- properties of radio waves
- radio waves have lower frequencies and longer wavelengths than microwaves.
- television uses higher frequencies than radio
- A radio programme does not need to be directly in view of the transmitter to receive signals
- for low frequency, radio waves, diffracion allows waves to be bent around tall buildings and obstacles.
- radio waves are used mainly for communications
- radio waves are EM radiation with wavelengths longer than 10cm
- different wavelengths of radio wave, refract and diffract in different ways
- long wave radio (wavelegnths of 1-10km) can be diffracted around the curved surface of the earth
- Key Information long wave signals can be diffracted around the earth!!
- radio waves that are used for TV and FM radio, are very short... (10cm -10m) to get reception,, you must be in direct sight of the transmitter
- short waves radio signals (about 10m-100m) can be recieved at long distances from the transmitter because of the waves being reflected off the ionosphere
- diffraction makes a difference to signal strength
- Diffraction-when waves spread out/apart when the waves pass through a gap or past an object....
- the amount of diffraction depends on the wavelegnth of the wave relative to the size of the gap
- longer wavelegnths can encounter a lot of diffraction, this means that the waves can bend around tall buildings ect.
- as a result of this, waves with longer wavelegnths can travel FURTHER between the transmitter and reciever.
- Because of this they DO NOT have to be in line of sight with each other...
- as a result of this, waves with longer wavelegnths can travel FURTHER between the transmitter and reciever.
- shorter wavelength radio waves, do not diffract as much...
- ... as a result, transmitters need to be located high up in order to avoid obstacles.
- some area have trobule recieving shorter wavelegnth radio signals
- Diffraction-when waves spread out/apart when the waves pass through a gap or past an object....
- refraction is also affected by wavelength
- when a wave come up against something of a different density, it changes speed... if the wave hits the new substance at an angle, it changes direction..... this is called rerfraction
- when this happens high up in the atmosphere, it can travel further for long distance communications
- radio waves travel faster through ionised parts of the atmosphere than non ionised parts. this causes refraction...
- short waves and medium wave radio signals are refracted mostly in the ionosphere- these are effectively reflected back to earth...
- the amount that a wave is refracted in the ionosphere depends on its frequency and angle of elevation...
- >short wave radio doesnt refract as much as medium wave...
- radio waves bounce off the ionosphere
- refraction is not always good... it can disrupt a signal by bending it away from the receiver dish...
- when a wave come up against something of a different density, it changes speed... if the wave hits the new substance at an angle, it changes direction..... this is called rerfraction
- digital radio helps reduce interferance
- radio stations often broadcast using similar frequencies because there's a limited number of radio wave frequencies that can be used to transmit a good digital signal
- as a result, many analogue signals suffer from interference because of this
- noise-similar waves covering a similar area combine
- DAB(digital audio broadcast) works different to traditional radio- the signal is digital from the start
- DAB
- with DAB, many different signals are compressed and transmitted as a single wave.... this is called multiplexing...
- many signals are transmitted along a small frequency bandwidth, and separated out at the end by receivers
- DAB suffers less interference than normal radio, and thanks to multiplexing many stations can broadcast at the same frequency
- even if you receive DAB, often the sound quality is affected because of signal compression
- long wavelengths travel well through earth atmosphere...
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