| 摘要 |
PURPOSE:To improve the deterioration in the reception side code error rate by detecting a level difference between base band signals inputted to an orthogonal amplitude modulation means by a level difference detection means and controlling the gain of either amplification means automatically so that the level difference is made zero. CONSTITUTION:Inputted base band signals of Ich and Qch are fed via low pass filters 21, 31, attenuators 22, 32 and amplifiers 23, 33 to an orthogonal amplitude modulator 51, where the carrier is subject to multi-value QAM modulation and the result is sent. In this case, parts of the base band signals of Ich and Qch inputted to the orthogonal amplitude modulator 51 are detected respectively by detectors 42, 45 via buffer amplifiers 41, 44 with a high input impedance, integrated by integration devices 43, 46, compared by a comparator 47, a differential signal is extracted, fed to an attenuator 22 via a choke ch and the attenuation is automatically controlled so as to make the difference signal zero. Thus, the deterioration of the code error rate of the reception side caused by the level difference of the base band signals of Ich and Qch is improved. |
