The Electromagnetic Fountain

Karl Jansky’s antenna

with 2 comments

Karl Guthe Jansky
Born: Norman Oklahoma October 22, 1905 (d.Feb.14, 1950)
Education: Graduated with a degree in physics from the University of
Joined Bell Telephone Laboratories in Holmdel, NJ, in 1928.

Bell Labs wanted to investigate using “short waves” (wavelengths of about 10-20 meters) for transatlantic radio telephone service. He was assigned the job of investigating the sources of static that might interfere with radio voice transmissions.

He built an antenna designed to receive radio waves at a frequency of 20.5 MHz (wavelength about 14.5 meters). It was mounted on a turntable that allowed it to rotate in any direction, and was nicknamed “Jansky’s merry-go-round”.

antenna

(image source: http://www.nrao.edu/whatisra/images/jansky1min.gif)

By rotating the antenna, it was possible to find what the direction was to any radio signal. After recording signals from all directions for several months Jansky identified three types of static:

  • Nearby thunderstorms
  • Distant thunderstorms
  • A faint steady hiss of unknown origin

He spent over a year investigating the third type of static, which rose and fell once a day such that he thought that what he was seeing radiation from the Sun. After a couple of months of following the signal, the brightest point moved away from the position of the Sun. The signal occured not every 24 hours, but every 23 hours and 56 minutes – characteristic of the fixed stars, and other objects far from our solar system. He eventually figured out that the radiation was coming from the Milky Way and was strongest in the direction of the center of our Milky Way galaxy, in the constellation of Sagittarius.

Jansky wanted to follow up on this discovery and investigate the radio waves from the Milky Way Galaxy in more detail. He proposed to Bell Labs to build a 30 metre diameter dish antenna. However, Bell Labs had the answer they needed already, that the static was not a problem for transatlantic radio communication. Jansky was assigned to another project ……

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Written by ajsteggell

May 5, 2007 at 12:16 am

2 Responses

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  1. Nice blog. Nice frog! I want the pants.

    Dean Whitbread

    May 5, 2007 at 8:18 am

  2. Me too! but I’d rather they worked!

    ajsteggell

    May 5, 2007 at 11:51 pm


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