User Manual DDS200 Digital Demodulation System 070-9952-00

Manual OperationFirst, a constellation diagram is shown, representing a very clean 64QAM signal(see Figure 2–47).Figure 2–47: Constellation diagram of ideal 64QAM signalThe following are examples of modulation errors and the resulting constellationdiagrams:Amplitude ImbalanceAmplitude imbalance describes the different gains of the I and Q componentsof a signal. Such a difference in amplitude is caused by different gainin the two signal paths (I and Q) of the transmitter. In a constellationdiagram, amplitude imbalance shows by one signal component beingexpanded and the other one being compressed. This is due to the fact that thereceiver AGC makes for a constant average signal level. See Figure 2–48.DDS200 Digital Demodulation System User Manual 2–63