| 摘要 |
PURPOSE:To enable to reject echo, by converting the amplitude-frequency characteristics at the intermediate frequency region by means of discrete Fourier inverse- transformation and calculating and sequentially erasing the parameter relating to a plurality of reflection waves. CONSTITUTION:The amplitude change of signal at the intermediate frequency stage is detected at the amplitude detector 6 and instantaneous frequency displacement of signal is detected at the frequency duscriminator 4 and this is input to the amplitude-frequency characteristics detection circuit 10. Further, this output is input to the discrete Fourier inverse-transformation circuit 11 for the transformation and it is fed to the weighting control circuit 7. Further, at the weighting control circuit 7, the inversion coefficient, delay time for a plurality of reflection waves, and phase difference between the direct wave and the reflection wave at the carrier frequency are detected. Further, in the weighting circuit 10, the amplitude of the tap output signal of the tapped delay circuit 8 is changed based on this phase difference. Further, the output signal of the weighting circuit 10 and the intermediate frequency input signal are synthesized at the synthesis circuit 2. |
