Jansky's antenna was 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, earning it the
name "Jansky's merry-go-round". By rotating the antenna, one could find
what the direction was to any radio signal. Reber's telescope had a
mirror, made of sheet metal 31.4 feet in diameter, that focused radio
waves
to a point 20 feet above the dish. A cylinder contained the radio
receiver which amplified the faint cosmic signals by a factor of many
million, making them strong enough to be recorded on a chart.
Reber built a parabolic dish reflector because this shape focuses waves to
the same focus for all wavelengths.
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