抄録
The standard frequency and time signal emissions in LF band began in 1999 in Japan. The bands of standard frequencies are rightly guarded from other intentional emission, but some reports show radio noise interferes with the receipt of the time signals. We observed LF band at several points, and found high level noises overlap at the some percents of time sequence. And additional search shows radio noise has two type origins. One is natural source, thunder noise, and it emits impulsive noise. But the other one, artificial origin, maintains emission during the origin works, and sometime becomes a strong disturbance.
