Information in Radio Waves
Teaching Note: ”Information in Broadcast Transmission”
Cover: Information Encoding in EM Radiation
Slide 1: Natural Sources of EM radiation
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Review the fundamental properties of electrons and protons.
Slide 2: The Electric Field
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Figure 1- static electric field produced by a single negative charge
Figure 2- Dipole field
Review the properties of fields and the use of field lines as vectors that represent the
field direction and strength
Slide 3: Electromagnetism Basics
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In this slide you may discuss the interaction of the electric and magnetic fields. It may
help to provide background on how materials may be naturally magnetic. Here is a good
reference, http://www.rare-earth-magnets.com/t-magnetism.aspx
It is important to define the transverse wave as a wave in which the field vectors are
oriented perpendicular to the direction of energy propagation.
You can also introduce wavelength and frequency here.
Slide 4: E field and B field
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It is interesting to discuss the fact that EM waves (light) do not accelerate. Once a
photon is generated it is immediately travelling at the speed of light.
Slide 5: EM Transmission
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Remind students of the game “Soy, Sugar, Glue” form the “Information Theory” unit.
Information was transmitted but it could only take the form of three words. Those were
the rules. Ask students, where there any other transmission channels that became
useful as the game went on. For instance, tone of voice, speed of speech, volume!.
 Here is a good resource on radio transmission
o http://galileo.phys.virginia.edu/classes/241L/emwaves/emwaves.htm
Slide 6: "Rules" of the EM transmission channel
 These are the four ‘ways’ in which EM radiation can be modified with examples
Slide 7 : Amplitude modulation
Information in Radio Waves
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Amplitude is analogous to Volume in Sound waves. It represents intensity which is
physically the # of photons of EM radiation.
Define carrier wave as the constant wave form. A signal wave is added to the carrier
wave to produce and interference pattern.
In this case the frequency is constant and only the amplitude is changing
This is easily interfered with in the environment and that is why you get so much static
on AM stations, especially during the day.
Slide 8: Frequency Modulation
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Define frequency modulation as amplitude being help constant an only the frequency is
modified.
Slide 9: Phase changes
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Demonstration of phase shifting
Slide 10: PHET simulation
Slide 11: Phase modulation
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Review the index of refraction and define attenuation (in this case a loss of amplitude)
Light travelling near strong gravitational field can be affect in the phase.
Slide 12: Polarization
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Define linear and circular polarization
Demonstrations with two diffraction gratings or polarized films and a light source is very
effective for illustrating these.
Slide 13 and 14: Information in the polarization
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Some real world examples of polarization
Slide 15: Information in polarization
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The degree of rotation of a polarized signal can yield information about the medium
through which the radiation has travelled