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Electromagnetic%20Wave%20Propagation

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Title: Electromagnetic%20Wave%20Propagation


1
Electromagnetic Wave Propagation
  • High School Science Demonstration
  • Melanie Leong
  • June 25, 2003

2
Early Radio to Radio Astronomy A Brief History of
Radio A Quick Introduction to Radio Astronomy
  • Onizuka Visitor Center Presentation
  • Melanie Leong
  • July 5, 2003

3
Agenda
  • Brief History of Radio
  • Explanation of Electromagnetic Waves and
    Frequency
  • Electromagnetic Wave Propagation - Spark Gap
    Generator
  • Quick Introduction to Radio Astronomy

4
A Brief History of Radio
  • Radio is a new subject in terms of science
    astronomy
  • We receive transmitted radio waves for enjoyment,
    entertainment, and information
  • 100 years ago Radio, as we know it, did not
    exist.
  • 1884, James Clerk Maxwell
  • Calculated the speed electromagnetic waves travel
    is approximately the speed of light.
  • Visible light forms only a small part of the
    spectrum of electromagnetic waves.

5
History of Radio (p2)
  • 1888, Heinrich Hertz
  • Proved that electricity could be transformed into
    electromagnetic waves.
  • These waves travel at the speed of light.
  • 1896, Guglielmo Marconi
  • Built a wireless telegraph, a spark gap
    transmitter receiver
  • On December 12, 1901, accomplished the Atlantic
    Leap from Poldhu, Cornwall, England to Signal
    Hill, Newfoundland

6
History of Radio (p3)
  • 1900, Reginald Fessenden
  • Continuous Waves necessary to transmit speech and
    music
  • December 23, 1900, First wireless voice message
    to colleague
  • Hello Brant.
  • One. Two. Three. Four.
  • Is it snowing where you are Mr. Theissen?
  • If it is, telegraph back and let me know.
  • Transmit and receive stations were only 1 mile
    apart, but this heralded the beginning of radio
    telephony.
  • On Christmas Day 1906, Ships 100 miles away heard
    Fessendens voice and O Holy Night playing on
    their morse code receivers.
  • 1906-1912, Radio Broadcast Development

7
History of Radio (p4)
  • 1924, Spark transmission was phased out
  • 1870s-1920s, Telephone developed and in service
  • 1932, Karl Jansky
  • While doing research for Bell Labs for
    transatlantic radio service, he observed radio
    waves coming from the center of the Milky Way
    Galaxy.
  • Not allowed to investigate more . . .
  • 1941, Grote Reber
  • In 1933, Read about Janskys work, published in
    the NY Times
  • By 1939, Built the first radio telescope in his
    backyard
  • By 1941, Measured and recorded the first radio
    sky map

8
Grote Rebers Radio Sky Maps
9
What are Electromagnetic Waves?
  • An electromagnetic wave is an energy wave
    produced from an electrical discharge.
  • Electromagnetic waves have rise and fall cycles.
  • The number of rise and fall cycles per second is
    its frequency.
  • We cant see or feel them, but they are around us.

10
Explanation of Frequency
  • Everything you see, and cant see, resonate at a
    specific frequency.
  • Frequencies are sinusoidal waves.
  • Speed of Light Frequency x Wavelength
  • Example The wavelength of a signal resonating
    at 3kHz is
  • 3 x 108 m/s 100 kilometers or 62 miles!
  • 3 x 103 Hz
  • Lower frequencies have longer wavelengths. This
    characteristic allows these frequencies to be
    used for Morse code and amateur radio.

11
Diagram of Waves Frequency
12
Frequency Bands

13
Simple Demo
  • Reviewing what we know
  • Electromagnetic waves propagate through space.
  • If there is an excitation - electrical discharge,
    what do you predict will happen?
  • Electromagnetic waves will propagate from its
    source to throughout the room.
  • That means a detector placed anywhere in this
    room will indicate that the waves have propagated.

14
Diagram of Demonstration

ignition coil
-
key

radio
battery
15
Field Coverage
  • This spark gap generator transmits broadband
    emissions - It covers a large band of
    frequencies.
  • With a radio tuned to an AM or Shortwave station,
    noise will be heard when the spark gap
    transmitter is energized. (530kHz to 4200kHz)
  • Tune to another AM/Shortwave station, you should
    get the same electrical discharge noise.
  • If the signal is regulated, or tuned, to one
    band of frequencies, communication can be gained.

16
Field Coverage (p2)
  • If there is a powerful discharge and you walked
    outside and down the street. Will the noise
    still be detected? Yes!
  • Which is why full time activation is prohibited
    by the FCC.

17
EM Wave Summary
  • Electromagnetic Wavelength - Distance of One
    Cycle (peak to peak)
  • Electromagnetic Frequency - Number of Cycles in
    One Second
  • Speed of Light Wavelength x Frequency
  • Electromagnetic Waves propagate through space
    from an electrical discharge
  • Electromagnetic Wave Propagation Uses -
    Communications, Astronomy, and much more

18
What is Radio Astronomy?
  • It is the study of electromagnetic emissions from
    celestial objects in the radio spectrum band.
  • Atoms and molecules in space emit their own
    unique electromagnetic waves.
  • Radio telescopes can see cold objects, they do
    not emit light
  • Able to detect radio sources behind interstellar
    clouds hidden from optical viewing.
  • Can detect distant galaxies at the edge of the
    Universe

19
CSO Atmospheric Transmission
20
350 µm Survey of Orion KL
21
Sagittarius A - Galactic Center
22
Arches Cluster in Sagittarius - Optical
23
Arches Cluster in Sagittarius - Radio
24
Sagittarius Arches in Optical Radio
25
Sgr Arches in Optical X-Ray/IR
26
Sagittarius - Arches Cluster
Optical
X-Ray/Infrared
Radio
27
(No Transcript)
28
Summary
  • Theres much more out there than visible light.
  • What is seen in radio waves is very different
    than optical.
  • Electromagnetic waves detected by Radio
    Telescopes tell us more about what else is going
    on out there.
  • All spectrum bands are used to observe, measure,
    and interpret what is going on out in the
    Universe.
  • Many different ground based and space based
    telescopes are made to accomplish this.
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