STUDY OF EFFECTS AND DEGREES OF ERROR OF MODULATION-DEMODULATION.
Final technical rept., for Mar-Sep 64,
CBS LABS STAMFORD CONN
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A theoretical study of three modulation-demodulation methods for use in the VGH recorder was conducted. Emphasis was placed upon the suitability of each system for providing increased accuracy over low speed direct tape recording. The methods investigated were 1 frequency modulation, 2 pulse duration modulation and 3 digital coding. The study included a general spectrum analysis, the signal-to-noise improvement available, and aliasing effects. Characteristics of each method investigated in the frequency modulation system -- the effect of an imperfect limiter and the use of a multivibrator modulator and pulse averaging discriminator in the pulse duration modulation system -- the comparator method of generating the signal in the digital system -- analogto-digital and digital-to-analog conversion was analyzed with regard to sampling effects and conversion inaccuracies. A seven-pole Butterworth low pass filter of the active type was designed and constructed to eliminate the aliasing problem. Laboratory performance proved suitability of the unit for use as an input filter. Author