# Chaos, Communication and Consciousness Module PH1

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```					Chaos, Communication and
Consciousness
Module PH19510

Lecture 6
Overview
   Theoretical Beginnings
   First Transmission
 Hertz
   Practical Systems
 Marconi,   Tesla, Braun
   Transmitting Information
 CW
 Amplitude   Modulation
   Chemist, Physicist
   Discovered
electromagnetic
,
induction
   Changing current in a
one coil induces
current in another
  N
dt
James Clerk Maxwell (1831-1879)

   Mathematician
   Brought together work
Ampere
   1864 presented
“Maxwell’s Equations”
Maxwell’s Equations

  H  0
H
  E  
No magnetic                            t
monopoles                  Changing magnetic
fields
E                 Electric fields
H  J                       E  
#    t
Changing Electric fields     Electric Charges
 Magnetic fields          Electric Fields
Divergence ·
 Scalar quantity
 Measure of ‘outgoingness’ of field at a
point
 Flow across boundary of infinitesimally
small sphere at point.
 Expansion  +ve divergence
 Contraction  -ve divergence
Curl ×
   Vector
 Rate of rotation of a field
 Points along axis of rotation
 Right hand rule
   Example
 Uniform  rotation
 Constant curl
 Points into page
Maxwell’s Equations

  H  0
H
  E  
No magnetic                            t
monopoles                  Changing magnetic
fields
E                 Electric fields
H  J                       E  
#    t
Changing Electric fields     Electric Charges
 Magnetic fields          Electric Fields
Consequence of Maxwell’s
Equations
   Electric and Magnetic
   Wave nature of             c

electromagnetism
Showed waves moved at
 0 0
speed of light
   Suggested light was form
of electromagnetic wave
   1873 Suggested
propogation of EM waves
Heinrich Rudolf Hertz
   1857 – 1894
   1887 Proved
Maxwell’s proposition
that Electromagnetic
Waves can travel
over distance
Hertz’s Experiment
1 – Primary circuit          Interrupter
Capacitor
•Current flows
through coil
• magnetic field in
core
• Interrupter Opens
Battery                •Current dies away
• magnetic field
dies away
•Interrupter Closes
•Current Flows
•(repeat forever)

Primary Coil   Core
Hertz’s Experiment
Secondary     2 – Secondary Circuit
Coil
Antennae
Plates
   Many turns in secondary
coil
   Changing field in primary
coil & core
    Very high voltage in
secondary (10-20kV)
   Sparks
Electromagnetic field
Spark Gap                 from antennae plates
Hertz’s Experiment

   Electromagnetic field
   (Tiny) sparks appear in
gap
Need to make communications
system
   Spark transmitter produces broad band
output
 Splash across many frequencies
 Due to rapid edge of spark

   Tiny sparks only visible in dark
The coherer
 Tube filled with silver/nickel filings
 Particles stick together (cohere) under
influence of electric field
 Allows large current to flow
 Unstick particles mechanically (hammer)
 Primitive amplifier
Nikola Tesla (1856-1943)
   1893-1895
Investigated high
frequency Currents
   Produced reliable
generator
   ‘Narrow’ frequency
band
Guglielmo Marconi (1874-1937)
   1896 Demonstrates
wireless telegraphy
 Resonance
 Coherer

   Extensive use in
ship/shore comms
The Cat’s Whiskers
   Karl Braun
 1874  Discovered point contact semiconductor
junction
 1898 Cat’s Whisker
 Simple Rectifier
 Phosphor Bronze spring contact
CW Modulation
   Continuous Wave
Carrier
   Turn carrier On & Off
   Transmit information
by length & timing of
On/Off periods
   Morse code
   Simple Digital
Antenna
   Voltage induced in
antenna by EM wave
Variable               Coil                             Variable Capacitor &
Capacitor                      Diode      Earpiece
primary coil select
required freq.
Capacitor                 Diode & capacitor
remove RF
   Signal heard in
Ground
earpiece
Amplitude Modulation - AM
   Transmit analogue signals – speech/music
   Same as Frequency Division Multiplexing
   Change amplitude of carrier depending on signal
   Multiplication process:

Transmitted  Carrier  (1  ModulationDepth  Signal )
Amplitude Modulation #1
   Carrier Waveform
1
0.951

0.5

Carrier( t im )     0

0.5

0.951      1
1 10       2 10              3 10       4 10       5 10
5           5                  5           5          5
0
0                            t im
5 10 5
Amplitude Modulation #2
   Signal Waveform
1
1

0.5

Signal ( t im )     0

0.5

1     1
1 10       2 10              3 10       4 10       5 10
5           5                  5           5          5
0
0                            t im
5 10 5
Amplitude Modulation #3
      Transmitted Waveform
Transmitted  Carrier  (1  ModulationDepth  Signal )
1.5
1.423

1
Modulation Depth x 2
0.5

Amp( t im )     0

0.5

1

1.423 1.5
1 10       2 10              3 10       4 10       5 10
5           5                  5           5          5
0
0                            t im
5 10 5
Demodulation of AM Signals

1.5
   Rectify signal with
1.423

diode
1
   Remove carrier with
Recovered( t im )
low-pass filter
0.5                                                                              Signal remains

0     0
1 10       2 10              3 10       4 10       5 10
5           5                  5           5          5
0
0                            t im
5 10 5
Overview
   Theoretical Beginnings
   First Transmission
 Hertz
   Practical Systems
 Marconi,   Tesla, Braun
   Transmitting Information
 CW
 Amplitude   Modulation

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