Construction of a 20 MHz Radio Telescope With Phased Dipole Antenna

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Construction of a 20 MHz Radio Telescope With
Phased Dipole Antenna

• Project by John Meyer

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Karl Guthe Jansky

• Jansky published a report in 1932 naming
  extraterrestrial sources as a cause of radio
  interference, effectively fathering the field of
  radio astronomy
• He spent two years collecting data from waves of
  20.5 MHz (14.6 m) with the array pictured to
  reach this conclusion
• Jansky was denied the chance to continue his
  research by his employer, bell Telephone
  laboratories, because they considered the
  question answered

http//www.astro.utu.fi/kurssit/ttpk1/ttpkI/Jansky
20_5MHz14_5mAntenna.jpg
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Grote Reber

• Reber built the first radio telescope for
  astronomical observation in 1937 at a cost of
  1,300 of his own money
• After years of failure, Success came in 1937 when
  he changed his receiver to collect waves of 1.87
  meters in length
• Rebers later work included a contour map of
  radio noise distribution in relation to the Milky
  Way

http//www.phys-astro.sonoma.edu/BruceMedalists/Re
ber/reber.jpg
http//www.nrao.edu/imagegallery/images/Reber_tele
scope_med.jpg
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Radio Jove

• The Radio Jove Program is a simple, low cost way
  to expose students to the thrills of radio
  astronomy
• The wavelength that the Radio Jove Kit is
  designed to detect is a wave of about 15 meters,
  frequently emitted by Jovian storms, especially
  in the presence of the moon Io, and by the Sun
  during the period when transitioning between
  sunspot cycles

http//www.enterprisemission.com/images/jupiter.jp
g
http//www.celestiamotherlode.net/catalog/sol.php
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The Dipole Antenna
E\Dir\Document\Ref\Jupiter.pdf Page 79

• The more dipoles there are in the array, the
  wider the section of the sky is that signals can
  be gathered from.
• The R-MC array in two dipoles arranged in the
  above fashion.

E\Dir\Document\Ref\Jupiter.pdf Page 72

• The dipole antenna is simply two equal lengths
  of wire separated by a small insulator
• The combined length of the dipole is half the
  wavelength of the wave a radio astronomer is
  trying to observe
• The dipole wire is made of a heavy gauge copper
  wire and the transmission line is coaxial cable

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The Dipole Equation

• This equation describes the potential of the
  dipole or how an electric field will effect the
  dipole
• q0 is the charge, is the angular frequency that
  the electrons are moving at, r is the distance
  from the source to the positively charged end of
  the dipole, and d is the distance from one end of
  the dipole to the other

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Beaming Pattern of Antenna
E\Dir\Document\Ref\Jupiter.pdf Page 78

• This picture represents the line of sight of
  the two dipole array it has two orientations,
  In-phase and Anti-phase
• In-phase means the sides of the dipoles that the
  center of the coaxial is connected to are both
  pointing in the same direction, examining the sky
  directly above the array
• Anti-phase means the dipoles are pointing in
  opposite directions and are observing two
  separate portions of the sky centered at 45
  degrees from straight up

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Phase 1 - Practice

• The first weeks of J-Term were spent practicing
  with soldering techniques
• The picture is of a circuit I built to test my
  soldering proficiency

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Phase 1 The Receiver

• Completed in the first week of Spring Term, this
  receiver interprets the signal coming from the
  antenna
• The receiver is composed of 97 different
  components, including Resistors, Capacitors,
  Inductors, Diodes, and IC chips, each which had
  to be soldered directly to the circuit board

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Phase 2 Antenna Construction
Construction of the array began around mid
semester after the final plan was chosen and the
dimensions set
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Phase 2 Array Completed
The structure pictured was designed to be rigid
enough to keep the dipole antenna up and straight
but flexible enough to not break in the event of
high wind
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Other Views

• A close up of the dipole center insulator
  (right)
• A straight on view of the array facing north
  (left)

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Example of Signal
These are solar bursts picked up by other
schools antenna similar to the one just
completed at R-MC
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Signals Received at R-MC
This signal was received during the testing phase
of the antenna. Set up for Solar observation at
the time, it is more likely that the antenna
picked this signal up from a communications
satellite.
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Signals Received at R-MC
This was a very weak signal that did not match
any example provided by Radio Jove. It sounded
like a carbonated drink.