Measuring the Linearity of Radio?Astronomy Receivers

Abstract

A convenient practice which is frequently adopted in observational radio 'astronomy is to express all aerial temperatures in terms of the temperature produced by a " point source" of known flux density. A difficulty with this procedure is that, with large telescopes and modern low-noise receivers, the aerial temperatures due to any of the better-known discrete sources are usually comparable with or greater than the receiver noise temperature. Under these <lircumstances, if the receiver response law is of the form (where D is recorder deflection, To is receiver noise temperature, and Ta is aerial temperature) the relation between Ta and D is in general non-linear, and in order to calibrate the receiver throughout its dynamic range we need to determine the form of the function f. D=f(To+TalIn principle this can be done by injecting a series of noise signals of known relative amplitudes at the receiver input and measuring the resulting recorder deflections. In practice, especially at high frequencies where the noise source is * Manuscript

A Study of the Decimetric Emission and Polarization of Centaurus A

“…A noise step coupled into the aerial feeder from an argon discharge tube was used as a transfer calibrator between the standard sources and the unknown sources. The receiver non-linearity was measured by applying this noise step in the manner described by Komesaroff and Mathewson (1962).…”