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.