2. » Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy ˃Science Practices ˃Core Idea ˃Cross-cutting concepts

3. » Lesson 1: EM modulation ˃Activity: make a simple radio ˃Activity: Build a cell phone detector » Lesson 2: AM and FM ˃Activity: Phet simulation » Lesson 3: Communications closure » Software Defined Radio Project (Summative)

4. Encoding information in radio waves Wikipedia Commons

5. » Take one nine volt battery, 1 nickle, and 1 AM radio. » Tune the radio to a region where you hear only static » Quickly Tap the nickel on the terminals of the battery » Record your observations in your notebook. » Take five minutes to investigate what factors might influence the system. » Reflection: Describe your observations and any relationships between variables in your system.

6. » 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 information? » How fast does your cell phone send information from one phone, through the base stations, and to another phone?

7. EM radiation is generated by the acceleration of an electron. properties of electron negative chargecharge almost negligible massmass (NIST, 1994) Wikipedia Commons

8. electron = elementary negative charge electric field decreases with distance according to an inverse- squared law exerts an electric force on other charged particleelectric force like charges = repulsion force opposite = attractive force note field lines are visual representation of field direction (arrows) and strength (line density) Figure 1. Figure 2.

9. Magnetism in materials also produces fields that influence (applies a force to) other magnetic materials magnetic fields can influence electric charges and likewise accelerating electric charges can create a magnetic field An accelerating charged particle produces both an electric field and a magnetic field that together form an electromagnetic disturbance that travels across distances as a transverse wave. Figure 1

10. » EM waves are variations in the electric field (E field) and magnetic field (B) over time. » These waves travel at a constant speed » C = 3.00 x 10 9 m/s

11. An EM wave carries both energy and information from one part of the universe to another. Therefor EM radiation constitutes a transmission channel! remember Sugar, Soy, Glue; the rules of your robot transmission channel?

12. These are the ways that the properties 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) Polarization (radio astronomy)

13. Two types of polarization » Linear polarization ˃Either vertical or horizontal » Circular polarization

14. » Phase shifting cannot be seen by the eye ˃Here the crest and trough are colored to illustrate +in phase waves +out of phase waves » Detecting phase changes In-phase Out-of-phase Wikipedia Commons

15. » How can the amplitude of an EM wave be changed? ˃Amplitude corresponds to intensity (# of photons) ˃Amplitude modulation stores a signal in a single frequency radio wave (carrier wave) Berserkerus/Wikimedia Commons

16. » Carrier wave ˃One frequency that will be added to by the signal frequencies » Signal Frequency ˃Contains the information from the source Berserkerus/Wikimedia Commons

17. » Starter » In a group of 2 or 3, collect answers to the following questions and chose 1 member to be a spokesperson. 1.Give some numbers of radio stations in our area. 2.What is your favorite station and why. 3.What do the numbers stand for? 4.Do you know where the transmission tower is?

18. » See “The History of Radio” for a full back ground on the developments in the 19 th and 20 th century that have led to our current technological communication. » Most common form of communication occurs on AM and FM (Frequency Modulated) carrier waves. » Lets look at how the information gets “encoded”

19. » How can the amplitude of an EM wave be changed? ˃Amplitude corresponds to intensity (# of photons) ˃Amplitude modulation stores a signal in a single frequency radio wave (carrier wave)

20. » Carrier wave ˃One frequency that will be added to by the signal frequencies » Signal Frequency ˃Contains the information from the source Note: Amplitude is not changing but frequency is (Frequency Modulation)

21. Pros » Very easy to detect with simple equipment (less expensive) » Narrow band width allows for more stations in a geographical area without interference. » Can be transmitted over long distances due to ionospheric refraction.

22. » Can be very noisy ˃Affected by electrical activity in the atmosphere ˃Affected by other radio transmissions » Fluctuates between day and night ˃Night time allows for long range transmission ˃HAM radio utilizes this » Broadcast transmissions would interfere with each other

23. » A carrier wave is generated at a source with a certain power. ˃This process required that a very consistent oscillation is generated in a current. ˃The frequency of the alternating current generated radio of the same frequency. » A Transmitting station adds a sound spectrum to the carrier wave

24. » 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 stations per geographic area

25. » Watch this short video clip about how information is encoded using frequency modulation » https://www.youtube.com/watch?v=SmW4z76KgNQ https://www.youtube.com/watch?v=SmW4z76KgNQ

26. » FM transmitters 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 watts ˃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 communication was done. …..Advertising time was sold to cover the cost.

27. » Here Here

29. Voice contains a spectrum of frequencies Vibrations from the air molecules strike a small transducer (microphone) The transducer changes the energy from molecular air motion to an electric current The current varies in magnitude on the same exact frequency as the voice did also That “signal” can be encoded onto a radio “carrier” wave. The radio carrier + signal is amplified to > 1000 W We pick up that radio wave when we tune a receiver to the frequency of the carrier The receiver then subtracts the carrier to get the signal Then the current is attached to a speaker which ‘wiggles’ a magnet at the same frequency as the original sound. The wiggling magnet finally creates the compressional waves that eventually reach our ears.

30. » So, now you know how radio waves are produced, but how do they carry things like voice, TV video, data from spacecraft etc….?

31. » Interaction with material or fields (electric, magnetic, or gravitational) as it travels.

32. » Human eyes are not sensitive to polarization » Polarized sunglasses work by excluding reflected and scattered light preferentially since they tend to be polarized in certain directions Polarized sunglasses

33. » Some animals (e.g. bees, ants, fish, octopuses, crickets) are sensitive 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)

34. » In radio astronomy the degree of rotation of a polarized signal (Faraday rotation) gives information about the density of material along the path of the signal.Faraday rotation

35. Satellite communication frequently makes use of polarization to send two separate non- interfering signals at the same frequency

37. » We have covered basics of wave theory. » The ways in which radio waves can be modified » From voice to radio and back to voice.

38. 1."Astronomy: A Beginner's Guide to the Universe" 7th ed. Chaisson, E.; McMillan, S. Pearson Education inc. 2013 p.503 2."Mass of an Electron." Fundamental Physical Constants. NIST, Oct. 1994. Web..http://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.

39. 4.Course: ASTR 122: Birth, Life and Death of Stars http://jersey.uoregon.edu/~imamura/122/astro.122.h tml http://jersey.uoregon.edu/~imamura/122/astro.122.h tml 5.http://www.pbs.org/wgbh/aso/tryit/radio/indext.htmlhttp://www.pbs.org/wgbh/aso/tryit/radio/indext.html 6.http://galileo.phys.virginia.edu/classes/241L/emwaves /emwaves.htmhttp://galileo.phys.virginia.edu/classes/241L/emwaves /emwaves.htm 7.http://www.astro.utu.fi/~cflynn/astroII/l4.htmlhttp://www.astro.utu.fi/~cflynn/astroII/l4.html