»  Communicate technical informa0on about how some technological devices use the principles of wave behavior and wave interac0ons with ma8er to transmit and capture informa0on and energy ˃  Science Prac0ces ˃  Core Idea ˃  Cross-­‐cu>ng concepts »  Lesson 1: EM modula0on ˃  Ac0vity: make a simple radio ˃  Ac0vity: Build a cell phone detector »  Lesson 2: AM and FM ˃  Ac0vity: Phet simula0on »  Lesson 3: Communica0ons closure »  SoJware Defined Radio Project (Summa0ve) Encoding informa0on in radio waves Wikipedia Commons
»  Take one nine volt ba8ery, 1 nickle, and 1 AM radio. »  Tune the radio to a region where you hear only sta0c »  Quickly Tap the nickel on the terminals of the ba8ery »  Record your observa0ons in your notebook. »  Take five minutes to inves0gate what factors might influence the system. »  Reflec0on: Describe your observa0ons and any rela0onships between variables in your system. »  How does your voice travel through space from your cell phone to your friends cell phone? »  What are two ways in which radio waves can be modified to carry informa0on? »  How fast does your cell phone send informa0on from one phone, through the base sta0ons, and to another phone? EM radia0on is generated by the accelera0on of an electron. proper0es of electron nega0ve charge almost negligible mass •
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Wikipedia Commons
(NIST, 1994)
electron = elementary nega0ve charge electric field •
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Figure 1.
decreases with distance according to an inverse-­‐
squared law exerts an electric force on other charged par0cle like charges = repulsion force opposite = a8rac0ve force note field lines are visual representa0on of field direc0on (arrows) and strength (line density) Figure 2.
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Magne0sm in materials also produces fields that influence (applies a force to) other magne0c materials magne0c fields can influence electric charges and likewise accelera0ng electric charges can create a magne0c field An accelera0ng charged par0cle produces both an electric field and a magne0c field that together form an electromagne0c disturbance that travels across distances as a transverse wave. Figure 1
»  EM waves are varia0ons in the electric field (E field) and magne0c field (B) over 0me. »  These waves travel at a constant speed »  C = 3.00 x 109 m/s An EM wave carries both energy and informa0on from one part of the universe to another. Therefor EM radia0on cons0tutes a transmission channel! remember Sugar, Soy, Glue; the rules of your robot transmission channel? •
These are the ways that the proper0es of waves can be affected by the radio source wether it be a natural source, or a man-­‐made Amplitude (AM radio) Frequency (or wavelength, FM radio) Phase (RADAR) Polariza0on (radio astronomy) •
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Two types of polariza0on »  Linear polariza0on ˃  Either ver0cal or horizontal »  Circular polariza0on In-phase
»  Phase shiJing cannot be seen by the eye »  Detec0ng phase changes ˃  Here the crest and trough are colored to illustrate +  in phase waves +  out of phase waves Wikipedia Commons
Out-of-phase
»  How can the amplitude of an EM wave be changed? ˃  Amplitude corresponds to intensity (# of photons) ˃  Amplitude modula0on stores a signal in a single frequency radio wave (carrier wave) Berserkerus/Wikimedia Commons
»  Carrier wave ˃  One frequency that will be added to by the signal frequencies »  Signal Frequency ˃  Contains the informa0on from the source Berserkerus/Wikimedia Commons
»  Starter »  In a group of 2 or 3, collect answers to the following ques0ons and chose 1 member to be a spokesperson. 1.  Give some numbers of radio sta0ons in our area. 2.  What is your favorite sta0on and why. 3.  What do the numbers stand for? 4.  Do you know where the transmission tower is? »  See “The History of Radio” for a full back ground on the developments in the 19th and 20th century that have led to our current technological communica0on. »  Most common form of communica0on occurs on AM and FM (Frequency Modulated) carrier waves. »  Lets look at how the informa0on gets “encoded” »  How can the amplitude of an EM wave be changed? ˃  Amplitude corresponds to intensity (# of photons) ˃  Amplitude modula0on stores a signal in a single frequency radio wave (carrier wave) »  Carrier wave ˃  One frequency that will be added to by the signal frequencies »  Signal Frequency ˃  Contains the informa0on from the source Note: Amplitude is not changing but frequency is
(Frequency Modulation)
Pros »  Very easy to detect with simple equipment (less expensive) »  Narrow band width allows for more sta0ons in a geographical area without interference. »  Can be transmi8ed over long distances due to ionospheric refrac0on. »  Can be very noisy ˃  Affected by electrical ac0vity in the atmosphere ˃  Affected by other radio transmissions »  Fluctuates between day and night ˃  Night 0me allows for long range transmission ˃  HAM radio u0lizes this »  Broadcast transmissions would interfere with each other »  A carrier wave is generated at a source with a certain power. ˃  This process required that a very consistent oscilla0on is generated in a current. ˃  The frequency of the alterna0ng current generated radio of the same frequency. »  A Transmi>ng sta0on adds a sound spectrum to the carrier wave »  Less noise from atmosphere ˃  Clearer signal \ »  Higher bandwidth Cons »  More local, long distance transmission difficult »  Interference from objects like buildings, mountains, etc… »  Wider bandwidth means less sta0ons per geographic area »  Watch this short video clip about how informa0on is encoded using frequency modula0on »  h8ps://www.youtube.com/watch?v=SmW4z76KgNQ »  FM transmi8ers are notoriously expensive to run ˃  They need complicated electronics to be able to encode the signal and carrier waves ˃  They need lots of voltage in order to increase power to > 1000 wa8s ˃  Need to be cooled, maintained, and serviced »  While the switch to FM was advantageous for the sound clarity and consistency, the expense requirements changed the way broadcast communica0on was done. …..Adver0sing 0me was sold to cover the cost. »  Here Voice contains a spectrum of frequencies The wiggling magnet finally creates the compressional waves that eventually reach our ears. Vibra0ons from the air molecules strike a small transducer (microphone) Then the current is a8ached to a speaker which ‘wiggles’ a magnet at the same frequency as the original sound. The transducer changes the energy from molecular air mo0on to an electric current The receiver then subtracts the carrier to get the signal The current varies in magnitude on the same exact frequency as the voice did also We pick up that radio wave when we tune a receiver to the frequency of the carrier That “signal” can be encoded onto a radio “carrier” wave. The radio carrier + signal is amplified to > 1000 W »  So, now you know how radio waves are produced, but how do they carry things like voice, TV video, data from spacecraJ etc….? »  Interac0on with material or fields (electric, magne0c, or gravita0onal) as it travels. »  Human eyes are not sensi0ve to polariza0on »  Polarized sunglasses work by excluding reflected and sca8ered light preferen0ally since they tend to be polarized in certain direc0ons »  Some animals (e.g. bees, ants, fish, octopuses, crickets) are sensi0ve to polarized light and use it to navigate and enhance their vision Left Panel presents a normal image of a soft plastic CD case with no polarization information.
Right Panel shows the image with polarization information. The finger print on the CD becomes clearly
visible.
(Nader Engheta, University of Pennsylvania)
»  In radio astronomy the degree of rota0on of a polarized signal (Faraday rota0on) gives informa0on about the density of material along the path of the signal. Satellite communica0on frequently makes use of polariza0on to send two separate non-­‐
interfering signals at the same frequency »  We have covered basics of wave theory. »  The ways in which radio waves can be modified »  From voice to radio and back to voice. 1.  "Astronomy: A Beginner's Guide to the Universe" 7th ed. Chaisson, E.; McMillan, S. Pearson Educa0on inc. 2013 p.503 2.  "Mass of an Electron." Fundamental Physical Constants. NIST, Oct. 1994. Web. <
h8p://physics.nist.gov/cuu/Constants/index.html>. 3.  “Outer Space is not Empty: A Teaching Unit in Astrochemistry”. RET 2004 Haystack Observatory MIT. Wesley Johnson and Roy Riegel. 4.  Course: ASTR 122: Birth, Life and Death of Stars h8p://jersey.uoregon.edu/~imamura/122/astro.
122.html 5.  h8p://www.pbs.org/wgbh/aso/tryit/radio/indext.html
6.  h8p://galileo.phys.virginia.edu/classes/241L/
emwaves/emwaves.htm 7.  h8p://www.astro.utu.fi/~cflynn/astroII/l4.html