GB797057A - Improvements in or relating to apparatus for frequency spectrum analysis - Google Patents

Abstract

797,057. Frequency spectrum analyses. TECHNICAL CERAMICS, Ltd. Dec. 12, 1955 [Dec. 17, 1954], No. 35627/55. Class 37. Apparatus for frequency spectrum analysis comprises first and second multipliers receiving a signal representing the frequency spectrum to be tested, together with sinusoidal and cosinusoidal voltages derived directly and through a quadrature phase shifter from a common variable frequency source; the multiplied outputs being applied to first and second integrating circuits time synchronized with each other, whose outputs are combined in a vectorial adder whose output represents an analysis of the input spectrum when displayed by an indicator means against successive values of the local source frequency. A voltage representing the frequency spectrum f(t) to be analysed is applied to the inputs of multipliers 2, 3 respectively energized by voltages representing sin 2#Ft and cos 2#Ft respectively, derived from variable frequency oscillator 4 directly and through quadrature network 5. The product voltages f(t) sin 2#Ft and f(t) cos 2#Ft are integrated with respect to time by circuits 6, 7 (controlled by frequency stepping timing circuit 8) whose outputs are combined in vectorial summation circuit 9 to a voltage representing the absolute evaluated Fourier integral for the individual line of the frequency spectrum, which is displayed as the y deflection of an oscilloscope of an x against y recording 10, whose x deflection is synchronized with frequency variations of the oscillator 4, so that by tuning the latter through the spectrum the amplitudes of the several component frequencies are displayed. If the spectrum is that of a pulse, the latter is stored on a tape or drum record and repetitively applied to the input; the oscillator frequency being shifted by a discrete value in synchronism with successive cycles of the record.