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Abstract

An FSK demodulator of the differential type is arranged to provide two versions of an input FSK signal that, relative each other, (1) have a linear phase shift versus frequency characteristic and (2) are phase shifted by 90 degrees at a center frequency halfway between the upper and lower FSK frequencies. The linear phase shift is provided by an N sample delay element, while a constant phase shift circuit which includes a K factor gain element provides the 90 degree phase shift. By virtue of this arrangement, the demodulator characteristics can be adaptively varied and the demodulator tuned simply by changing the value of K. A similar adaptive technique is applied to a threshold detector arranged to position a threshold midway between the extremes of an input signal.

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