The Advantest R3541A Modulation Accuracy Measurment is a companion unit designed for use with the R3265/R3271 Spectrum Analyzer family. The R3541A measures the modulation accuracy of Tone/4 DQPSK digital modulation in JDC or NADC digital radio systems. The R3541A consists of a down converter, high-speed digitizer, digital signal processor, and interface to the R3265/R3271.