The definition of APD limits for base-band digital modulation systems

Amplitude probability distribution (APD) statistical parameter measuring technique was approved as a new standard electromagnetic disturbance measurement method in CISPR16-1 Ed.2, but the limits of APD is still under consideration. Based on the constellation diagram, a general method to determine APD limits is presented in this paper. First of all, the smallest Euclidean distance of communication system is obtained from the constellation. Secondly, the relationship between APD and Bit Error Rate (BER) is established. As well as an example is given to show how to determine APD limits for a few base-band digital modulation systems. Finally, considering the APD limit based on the max BER is too strict to use in actual measurement, a method to obtain approximate average APD limits is presented and illustrated.