| 摘要 |
PURPOSE:To improve the demodulation performance with respect to a modulation wave having a large frequency shift by varying the frequency deviation characteristic of quadrature detection with respect to an FM pi/4 shift QPSK modulation carrier. CONSTITUTION:An inputted FM pi/4 shift QPSK modulation carrier reaches a constant envelope by a limiter 2, a peak level is digitally converted at a comparator 3 and fed to a monostable multivibrator 4. The signal is converted into a pulse signal with a time width being 1/4 of a period synchronously with a leading edge of the carrier and the signal is converted into a pulse signal with a time width being 1/2 of the period synchronously with a trailing edge of the carrier. When the signal is fed to a level converter 6, the signal is converted into an analog signal and it is fed to a delay detector 7, in which the signal is multiplied with a constant envelope signal from the limiter 2, and a demodulation signal reproduced corresponding to the frequency shifted signal. Thus, the demodulation performance of a modulation wave having a large frequency shift is improved. |
