A digital correlation receiver for the Gauribidanur Decametre wave radio telescope

Abstract

A low-frequency radio telescope operating at 34.5 MHz has been set up at Gauribidanur (Latitude: 13°36′12″ N, Longitude: 77°26′07″ E) in the form of a T-shaped array antenna. It consists of:

A 1.38 kilometre long array of 160 elements along the East–West line. A 90-element array extending southward from the centre of the East–West array.

When the output of the East–West array is correlated with that of the North–South array, a beam of 26′ in right ascension and 38′ in declination is produced. The telescope is a meridian transit instrument with the capability for tilting the beam in the meridian.

Digital Correlation Receiver System To take advantage of the aperture synthesis technique in mapping large regions of the sky in a single scan, a Digital Correlation Receiver System has been designed, constructed, and incorporated into the above-mentioned instrument. In this system:

The output of the East–West array is simultaneously correlated with each of the 90 spatial frequency components of the sky brightness distribution corresponding to the spacings of the North–South elements from the East–West array. A brightness distribution map for various zenith angles can then be computed by taking the inverse Fourier transform of the measured correlation coefficients.

Hardware and Processing

A fast, on-line, hardware Fourier Transform (FT) processor has been designed and constructed. The Digital Correlation Receiver System provides:

Delay and phase corrections Weighting of the correlation coefficients on an on-line basis

A microcomputer has been designed and constructed for use as a peripheral controller to:

Acquire the data from the FT processor Display the brightness distribution map on a video monitor Record the data on magnetic tape for further processing Field Trials The Digital Correlation Receiver System has been tested by carrying out field trials, and the results are presented.