Spectroradiometric analysis of radio signals
C. Snow · Scientific Papers of the Bureau of Standards · 1923
When a radiation, regularly repeated, is received by a simple circuit possessing inductance, capacity, and resistance there is induced in it an electric ctu-rent whose efFectiive value may be measiu-ed by a hot wire ammeter, provided the signal is repeated for a suflBcient time to take readings of the instrument, and provided that the time between the signals is very small compared to the period of the ammeter.If, while the radiation continues, the circuit be tuned to various frequencies in a certain range, and the current observed in each case, then these ciurent readings may be plotted against resonance frequency of the circuit.If the latter has a relatively high resolving power compared to the spectral structure of the wave, such a curve will be proportional to the spectral distribution of energy in the radiation.As a matter of fact this is not usually the case, and to derive the energy distribution of the wave requires that a certain integral equation be solved in which the above- mentioned curve is the known function.Several methods of obtaining a practicable solution of this equation are developed here and applied to experimental observations.The function of this paper is to develop a method of spectrum analysis which may be applied to the study of the interference-producing quality of a given sending station.CONTENTS.Page I. Introduction-Derivation of fundamental equation 231 II.First form of solution-Fomier's integral method 236 III.Second form of solution-^Adaptation for evaluation with a harmonic ana- lyzer 237 IV.Third form of solution-Operation with cos a D^2 44 V. Fourth form of solution-Empirical formula for the observed function . .251 VI.General relation by means of complex integration 256 VII.Application of fourth method to experimental curves 257 VIII.Conclusion 261 I. INTRODUCTION-DERIVATION OF FUNDAMENTAL EQUATION.The question as to what constitutes interference quality in a radio wave is one of such importance as to deserve both experi- mental and theoretical study.Undoubtedly a thoroughgoing spectrum analysis of the radiation when properly interpreted ought to furnish a logical basis for rating the interference-producing qualities of a sending station.It must be confessed that, in spite 231