A New Total-Difference Frequency-Distortion (TDFD) Meter Offering 135-dB Range and without Critical Filters
A TDFD meter which requires neither critical filter stages nor test signals, either from external sources or of high purity, is in beta production. Quadrature synchronous detectors, simple passive filters, and PLL-synthesizers give a measurement dynamic range of >135-dB or 0.15 ppm. The microprocessor displays TDFD, calculates THD, and shows odd- and even-order distortion fractions. The possibilities exist of locking-on to an external reference, allowing measurement of compact disc players, or of changing the test signal frequency by shifting the master reference. Large shifts will require canyon filters instead of notches.
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