Large 22-MHz array for radio astronomy

Abstract

The relative merits of T- and cross-type radio telescopes are discussed. A large array used for radio astronomical studies at a frequency of 22.25 MHz ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda = 13.5</tex> m) is described. It is built in the form of a T with dimensions <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">96\lambda \times 2.5\lambda</tex> east-west and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">32.5\lambda \times 4\lambda</tex> north-south. The 624 full-wave dipoles are mounted <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda/8</tex> above a 65 000 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> reflecting screen. The instrument has a pencil-beam response of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.1 \times 1.7</tex> degrees at the zenith. A timesharing technique is used to provide simultaneous observations of 5 adjacent declinations spaced at quarter-beamwidth intervals. Observations, commenced in 1965, should provide flux density measures for 400-500 radio sources down to a limiting flux density of about <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30 \times 10^{-26}</tex> W .m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . A map of the galactic background radiation from declination +90 to -20 degrees is being prepared.