Frequency deviation measuring device

Abstract

A frequency deviation measuring device is used in fields of digital mobile communication systems to measure frequency deviations with respect to .pi./4 QPSK modulation signals in accordance with the phase locus method. A center frequency is detected on the basis of a spectrum distribution measured with respect to a testing signal which corresponds to a digital modulation signal. A non-modulation signal is generated based on the center frequency detected from the testing signal. Quasi-synchronization wave detection is performed on the testing signal and non-modulation signal to produce an IQ base band signal. A first frequency deviation is detected based on the IQ base band signal in accordance with the phase locus method. A second frequency deviation is detected based on a difference between the center frequency and a testing frequency set value. The first and second frequency deviations are added together to provide a measured value of a frequency deviation between the testing signal and testing frequency set value. Because the quasi-synchronization wave detection is performed using the non-modulation signal based on the center frequency which is detected based on the spectrum distribution of the testing signal, it is possible to increase a range of measurement for the frequency deviation up to 1/5 or more of the symbol rate.

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