Channels of communication
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Transcript of Channels of communication
CHANNELS OF COMMUNICATION
Fig 1.
CHANNELS OF COMMUNICATION
Copper wiresWire pairsCoaxial cablesOptic fibresRadio wavesMicrowavesSatellites
COPPER WIRES
Fig 2.
COPPER WIRES Cheap Used in the first telephone networks (1876)
and still used today. Copper wires transmit electrical current. Current is not constant so produces variations
in magnetic fields. Variations in magnetic field produce cross –
talk. Cross – talk generates noise and interference. Copper wires need to be spaced apart to
reduce effects. Low bandwidth (20kHz). Frequent need for amplification (every 10km).
WIRE PAIRS
Fig 3.
WIRE PAIRS
Twisted wires carry currents in opposite directions.
Opposite currents reduces magnetic field interference.
Twisted wires reduce flux linkage. Minimizing area minimizes unwanted signals
created by electromagnetic induction due less exposure to other magnetic fields.
Problems with attenuation. Amplification needed every 5km.
Low bandwidth (500kHz). Distorts transmitted radio waves travelling in
wire of different frequencies and speeds due to dispersion.
COAXIAL CABLE
Fig 4.
COAXIAL CABLE Coaxial refers to the common axis of the two
conductors. Both conductors are parallel. Most common cable for transmitting TV and
video signals. Grounded shield protects core. Data is sent through central copper core. Electric and magnetic fields are confined
within the dielectric. Interference from outside noise is reduced by
outer shield, grounded shield and dielectric. Good at carrying weak signals. High bandwidth (500MHz) Amplification (MHz = 10km, GHz = 100m). Buried underground which is expensive.
OPTIC FIBRES
Fig 4.
OPTIC FIBRES
Replacing Coaxial cable High frequency signals (approaching THz) High bandwidth (10GHz) Low attenuation Amplification every 80km Perfect regeneration (Schmitt trigger)
RADIO SIGNALS
Fig 5
Fig 6
SURFACE RADIO WAVES
Frequencies of 3MHz, wavelengths ≤ 100m Diffracted by Earth’s surface, therefore
following the curvature of the Earth. AM radio transmissions can travel distances
of 100’s km. Powerful transmitters at low frequencies of
3kHz can travel 1000’s km.
Fig 7.
SKY RADIO WAVES
Radio waves of 3MHz up to 30MHz. Radio waves suffer total internal reflection. Wave travels a certain distance from transmitter called
‘skip distance’. ‘Skip distance’ is unreliable due to changes in ionosphere. Severe problems with attenuation. Huge interference due to ions ionosphere.
Fig 8
SPACE RADIO WAVES
Radio waves of frequencies above 30MHz. Waves travel in straight lines and are not
effected by ionosphere (λ = 10m). Used for Earth bound satellite transmissions,
FM transmissions and GPS.
Fig 9.
MICROWAVES
High frequency waves (GHz) Large bandwidth (100MHz) Multiplexing possible due to large bandwidth. Travel in straight lines, not effected by
ionosphere. Reduced attenuation.
Fig 10
COMPARISONS BETWEEN CHANNELS OF COMMUNICATION
ChannelCarrier Frequency
Bandwidth
Average distance between amplifers
Specific attenuatio
ndB /km
Copper wire
20kHz 20Hz 10km 10
Wire pairs 10MHz 500Hz 5km 25
Coaxial cable
2MHz (phone)
1GHz (TV)500MHz
10km
100m
6
200
Microwaves
5GHz 100MHz 50kmDistance – dependent
Optic fibres
0.2THz 10GHz 80km 0.20
SATELLITES
Fig 11.
GEOSTATIONARY SATELLITES
Equatorial orbit approximately 42000km above the Earth’s centre.
Expensive to put into space (1963). However ideal for communication.
Communication signals need to be in the range of GHz. Large bandwidth means multiplexing is possible. Limited power in satellite means that down-link signal
transmission must require low power signals. Up-link signals need to be powerful and have higher
frequencies than down-link signals.
GEOSTATIONARY SATELLITES
13 equatorial countries, 7 have equatorial space. Who owns the space?
1 geostationary satellite can cover 42% of the entire surface of the Earth.
3 geostationary satellites can cover the entire surface, not taking into consideration the polar caps.
POLAR SATELLITES
Orbits poles a few hundred km’s above Earth surface.
Can receive, store and retransmit data at a later time.
Cheaper to put into orbit and requires less power to up-link signals.
GPS
Fig 14.
SATELLITES
Communication to rural areas. Environmental concerns.
No more cables but increasing space junk. International understanding.
No international boundaries leading to international understanding. However there is always extremism
Colonizing space.
HIGH BANDWIDTH COMMUNICATION
Good points Multiple communications Sharing of information Business
Bad points Copyright infringement Extreme views Plagiarism Inappropriate material Spam
PHOTO URL’S Fig 1 -
http://gb.fotolibra.com/images/previews/214705-telegraph-poles-route-66-near-bluewater-nm.jpeg
Fig 2 - http://img.diytrade.com/cdimg/342538/1772020/0/1135589056/Single_Crystal_Copper_Wire.jpg
Fig 3 - http://image.made-in-china.com/4f0j00kBYQraIyVWbt/Station-Wire-With-One-Twisted-Pair-Conductors.jpg
Fig 4 - http://indolinkenglish.files.wordpress.com/2011/11/fiber-optic-cable-008.jpg Fig 5 -
http://www.sciencephoto.com/image/345583/large/T3000586-Radio_masts_with_radio_waves-SPL.jpg
Fig 6 - http://shariqa.com/E.M%20Wave%20Still.jpg Fig 7 - http://www.radio-electronics.com/info/propagation/ground_wave/ground_wave.gif Fig 8 - http://www.eoearth.org/files/155501_155600/155562/radio_transmissions.jpg Fig 9 - http://www.spaceweather.gc.ca/images/tech/effectsgps450.gif Fig 10 - http://zone.ni.com/cms/images/devzone/ph/ab273253214.gif Fig 11 - http://i.telegraph.co.uk/multimedia/archive/01514/SMOS_1514480c.jpg Fig 12- http://globalmicrowave.org/content/equitorial_orbit_geo.jpg Fig 13 - http://www.worldatlas.com/aatlas/newart/locator/equator.gif Fig 14 - http://globalmicrowave.org/content/polar_orbit.jpg
SOURCES OF REFERENCE
Hamper, C. (2009). Higher Level Physics developed specifically for the IB Diploma . Essex: Pearson Education Limited.
Tsokos, K.A. (2008). Physics for IB diploma, fifth addition. Cambridge: Cambridge University Press.