STUDY OF EFFECTS AND DEGREES OF ERROR OF MODULATION-DEMODULATION.
Abstract
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)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1965
- Accession Number
- AD0620673
Entities
People
- Edward J. Foster