This document discusses various channels of communication including copper wires, wire pairs, coaxial cables, optic fibers, radio waves, microwaves, and satellites. It provides details on each method such as the bandwidth, attenuation rates, and applications. Copper wires were the first communication system but have limited bandwidth. Optic fibers now provide the highest bandwidth for communication over the longest distances with the lowest attenuation rates. Satellites can provide communication coverage to both local and global areas depending on their orbit types.

1. CHANNELS OF
COMMUNICATION
Fig 1.

2. CHANNELS OF COMMUNICATION
Copper wires
Wire pairs
Coaxial cables
Optic fibres
Radio waves
Microwaves
Satellites

3. COPPER WIRES
Fig 2.

4. 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).

5. WIRE PAIRS
Fig 3.

6. 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.

7. COAXIAL CABLE
Fig 4.

8. 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.

9. OPTIC FIBRES
Fig 4.

10. OPTIC FIBRES
 Replacing Coaxial cable
 High frequency signals (approaching THz)
 High bandwidth (10GHz)
 Low attenuation
 Amplification every 80km
 Perfect regeneration (Schmitt trigger)

11. RADIO SIGNALS
Fig 5
Fig 6

12. 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.

13. 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.

14. 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.

15. 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.

16. 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

17. SATELLITES
Fig 11.

18. 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.

19. 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.

20. 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

21. 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.

22. HIGH BANDWIDTH
COMMUNICATION
Good points
 Multiple communications
 Sharing of information
 Business
Bad points
 Copyright infringement
 Extreme views
 Plagiarism
 Inappropriate material
 Spam

23. 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

24. 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.