Title: Electromagnetic Wave Propagation
1Electromagnetic Wave Propagation
- High School Science Demonstration
- Melanie Leong
- June 25, 2003
2Early Radio to Radio AstronomyA Brief History of
Radio A Quick Introduction to Radio Astronomy
- Onizuka Visitor Center Presentation
- Melanie Leong
- July 5, 2003
3Agenda
- Brief History of Radio
- Explanation of Electromagnetic Waves and
Frequency - Electromagnetic Wave Propagation - Spark Gap
Generator - Quick Introduction to Radio Astronomy
4A 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.
5History 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
6History 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
7History 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
8Grote Rebers Radio Sky Maps
9What 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.
10Explanation 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.
11Diagram of Waves Frequency
12Frequency Bands
13Simple 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.
14Diagram of Demonstration
ignition coil
-
key
radio
battery
15Field 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.
16Field 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.
17EM 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
18What 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
19CSO Atmospheric Transmission
20350 µm Survey of Orion KL
21Sagittarius A - Galactic Center
22Arches Cluster in Sagittarius - Optical
23Arches Cluster in Sagittarius - Radio
24Sagittarius Arches in Optical Radio
25Sgr Arches in Optical X-Ray/IR
26Sagittarius - Arches Cluster
Optical
X-Ray/Infrared
Radio
27(No Transcript)
28Summary
- 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.