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• 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.
• 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
• 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...
• 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
• 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...
• 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