The first solution to the regional clock synchronization problem was the Radio timing system developed by the United States in 1905, the beginning of modern timing technology.
In the short-wave band used by radio waves, the transmission of short-wave is easily interfered by the transmission media, and the transmission of radio waves through the atmosphere leads to the constant change of the transmission velocity with the atmosphere, resulting in the instability of the transmission delay. Therefore, the timing accuracy of short-wave band is low.
Although the disadvantages of short-wave transmission had been identified by radio operators at the time, and the difficulties associated with long-wave transmission could be overcome, it was not until about 1960 that long-wave transmission became widely used as a medium for time transmission.
