Large 22-MHz array for radio astronomy

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 (
\lambda = 13.5
m) is described. It is built in the form of a T with dimensions
96\lambda \times 2.5\lambda
east-west and
32.5\lambda \times 4\lambda
north-south. The 624 full-wave dipoles are mounted
\lambda/8
above a 65 000 m
²
reflecting screen. The instrument has a pencil-beam response of
1.1 \times 1.7
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
30 \times 10^{-26}
W .m
^-2
Hz
^-1
. A map of the galactic background radiation from declination +90 to -20 degrees is being prepared.