Discovery of microwaves leads to development of radio telescopes

Some magnetrons were handed over to NRC, which improved them and incorporated them into radar systems for the allies

In 1940 Britain was hard pressed defending itself, and did not have the resources to exploit important secret devices it had invented for the war effort. The British government decided to hand them over to Canada and the U.S.A., where the resources were available to continue their development.

One of the most closely-guarded of these secrets resembled a copper hockey puck with cooling fins, with two wires coming out of one edge, with a large connector opposite. This device, the resonant cavity magnetron, invented by John Randall and Harry Boot at Birmingham University, made it possible, for the first time, to produce high-power radio transmissions at short, centimetre wavelengths. Today we call these microwaves. That copper hockey puck made precision radar systems possible, using antennas ten or more times smaller than any existing systems. They could be deployed on aircraft, vehicles and ships. Earlier airborne radars required the plane to be covered in antenna components, making them look like flying hedgehogs. The new antennas could be little dishes concealed in the noses of the aircraft.

Some magnetrons were handed over to NRC, which improved them and incorporated them into radar systems for the allies, making the organization a major centre for wartime radar development. When peace returned, NRC found itself with a lot of accumulated expertise and a lot of radar hardware lying around. One of the NRC scientists working on radar development was Arthur Covington. In 1946 he and his colleagues used those components to make Canada’s first radio telescope. Its operating wavelength was 10.7 cm.

Over the following months, Canada’s first radio astronomers pointed their instrument at the Milky Way, planets, the aurora, the Moon and the Sun. However, the only cosmic radio waves they could detect came from the Sun.

Covington and his team noticed two key things. Firstly the solar radio emissions were stronger than expected, and secondly, they varied from day to day. Using a solar eclipse on 23 November, 1946, Covington found that most of the radio emission was coming from a magnetically active area on the Sun, and that the measurements he and his team were making were a stethoscope on solar magnetic activity.  Fortuitously, 10.7 cm is a very good wavelength for this. Since this magnetic activity affects our communications, satellite performance, GPS navigation, power lines, pipelines and many other human activities and infrastructure elements, Covington’s radio measurements became very important, and a service of providing these data, now known as the 10.7 cm solar radio flux, or F10.7, to users around the world.  NRC, now in partnership with Natural Resources Canada and the Canadian Space Agency, continues to make daily measurements of F10.7 and distribute them to the world. The programme is now located at the Dominion Radio Astrophysical Observatory, in B.C.

In the postwar years, the resonant cavity magnetron made possible one other key piece of technology that most of us have in our homes, the microwave oven.

Mars is low in the Southwest after sunset. Jupiter rises around 7 p.m. and Venus around 4 a.m. The Moon will be new on the 13th.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astro-physical Observatory, Penticton.

 

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