Statistical addition method for external noise sources affecting HF-MF-LF systems

The current statistical method for the addition of external component noise sources in the LF, MF, and lower HF band (100 kHz to 3 MHz) produces total median noise levels that may be less than the largest-component median in some cases. Several case studies illustrate this anomaly. Methods used to sum the components rely on their power (decibels) distributions being represented as normal by the statistical parameters. The atmospheric noise component is not correctly represented by its decile values when it is assumed to have a normal distribution, causing anomalies in the noise summation when components are similar in magnitude. A revised component summation method is proposed, and the way it provides a more physically realistic total noise median for LF, MF, and lower HF frequencies is illustrated.