Channels of communication

CHANNELS OF
COMMUNICATION

Fig 1.

CHANNELS OF COMMUNICATION

Copper wires
Wire pairs
Coaxial cables
Optic fibres
Radio waves
Microwaves
Satellites

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
 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

Fig 7.

 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.

SKY RADIO WAVES

Fig 8

 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.

SPACE RADIO WAVES

Fig 9.

 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.

MICROWAVES

Fig 10

 High frequency waves (GHz)
 Large bandwidth (100MHz)
 Multiplexing possible due to large bandwidth.
 Travel in straight lines, not effected by ionosphere.
 Reduced attenuation.

COMPARISONS BETWEEN
CHANNELS OF COMMUNICATION
Average
Specific
Carrier distance
Channel Bandwidth attenuation
Frequency between
dB /km
amplifers
Copper wire 20kHz 20Hz 10km 10
Wire pairs 10MHz 500Hz 5km 25
2MHz 10km 6
Coaxial
(phone) 500MHz
cable
1GHz (TV) 100m 200
Distance –
Microwaves 5GHz 100MHz 50km
dependent
Optic fibres 0.2THz 10GHz 80km 0.20

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

Fig 14.

 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

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
 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.

Channels of communication

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Channels of communication