in radio astronomy, an instrument for studying the spectrum of cosmic radio emissions received by a radio telescope. It is used principally to study radio spectral lines formed in the interstellar medium.
A radio spectrometer consists of a highly sensitive superheterodyne receiver, a spectrum analyzer, and a recording device. In the receiver, high-frequency electric oscillations caused by the radiation under study are amplified and converted to frequencies with which the analyzer can operate. Most widespread are multichannel analyzers with narrow-band filters tuned to various frequencies in the part of the spectrum being studied. At the output of each filter, a signal is registered that is proportional to the power of the electric oscillations passing through the filter. Radio spectrometers are usually provided with devices for eliminating the influence of continuous spectra from cosmic radio sources and for eliminating the effects of the receiver’s intrinsic noise.
The fundamental parameters of a radio spectrometer are the frequency-resolution Δfr and the sensitivity. In spectrometers equipped with filter analyzers, Δfr is determined by the frequency bandwidth of the narrow-band filters; depending on the width of the narrowest details of the spectrum under study, values of Δfr range from 102 to 106 hertz. The sensitivity is defined by the formula , where ΔP is the minimum measurable power encompassed in the band Δfr, α is a coefficient of the order of unity, P is the sum intensity of the receiver noise and the received radiation, and T is the integration time of the output signals expressed in seconds. In order to increase the sensitivity of a radio spectrometer, it is necessary to use low-noise quantum or parametric amplifiers and long integration times (up to several hours) for the output signals.
REFERENCESDrake, F. D. “Radioastronomicheskie priemniki i ikh kalibrovka.” In Teleskopy. Moscow, 1963. (Translated from English.)
Ryzhkov, N. F. “Apparaturnye metody radiospektroskopii mezhzvezdnoi sredy.” Astrofizicheskie issledovaniia, 1974, vol. 6.
N. F. RYZHKOV