The noise level and standard frequencies in the LF-band

We researched the electro-magnetic environment at standard frequencies in Japan. With the APD (Amplitude Probability Distribution) approach, if standard frequencies are received, the probability is constant for 60-70% in spite of increase of electric field intensity. Pulse duration measurements of time signals show another important element. The ratio of duration which coincides with time signals' is very low, but summing up neighboring durations comes up to the ideal ratio. However, such ratios depend on the slice level selected for calculating the duration time. The best place for slice levels is in a pocket of the distribution of the electric field intensity, which is the probability constant area of APDs. This pocket fluctuates up and down daily, and the best time for measuring time signals is midnight.