151. VIDEO-PRESENTATION ANALYZER 50 KC TO 10 MC
- Author
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NAVAL RESEARCH LAB WASHINGTON DC, GRIFFIN, F. T., NAVAL RESEARCH LAB WASHINGTON DC, and GRIFFIN, F. T.
- Abstract
Videofrequency spectra data, from the modulating source as well as the incorporated amplifier, of an electronic countermeasures equipment are often required in determining the equipments' effectiveness. Previous facilities utilized for video analysts were characterized by slow operational point-to-point sampling procedures, and by uncertainty of resolution figure due to possible Q variation of each of the multiple-tune circuits used in the analyzer. After a brief discussion on the merits and limitations of tuned circuit type analyzers as contrasted with superheterodyne types,a quasi-instantaneous video analyzer which was developed principally for the rapid analysis of modulation spectra is described. The instrument presents the frequency analysis of a complex voltage visually, with an alternative provision for instrumental analysis by manual control. it is essentially a double conversion superheterodyne receiver without preselection. A magnetically controlled local oscillator is used as a sweep for visually displaying the complete spectrum from 50 kc to 10 Mc, on a cathode ray tube. in addition, a manually tuned local oscillator is used in conjuction with a thermistor bridge indicator for a point-by-Point analysis. The superhoterodyne principle permits a suitable, constant, and controlled resolution value to be used, and allows a visual analysis to be made in 1/30 second by sweeping the local-oscillator frequency over the desired frequency band at a 30-cps repetition rate. A relation exists between the three factors - the video frequency band to be analyzed, the time required to give a complete analysis, and the final resolution bandwidth of the analyzer. For a video frequency band of 50 kc to 10 Mc, and an analysis time of 1/30 second, the minimum permissible resolution bandwidth is 17.5 kc.. The resolution may be increased by using a smaller video band to be analyzed, or by increasing the time permitted for a complete analysis.
- Published
- 1956