Space Weather Monitors- Stanford SOLAR Center

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How do I arrange for accurate timekeeping on my system?

(information provided by Chris Chapman)

Although SIDS can be monitored without extremely accurate timekeeping, timekeeping is critical for gamma ray bursts and some other phenomena. Although most computers provide 'software clocks,' these clocks can vary by over 10 sec per day.

There are a collection of on-line time services, although even these seem to be getting overloaded and errors of a second or more have been reported. To further complicate matters, the delay in getting the signal from the server to the SID location over a phone line may be variable. Analog channels do not tend to experience large delays, but digital ones may be less reliable.

One of the better services is About Time. This product runs in the background and can be set to update the PC clock from the internet every few minutes. It is reasonably accurate because it gets the time from a time server and then 'pings' the server to check the signal delay, which is adjusted accordingly.

The cheapest precision clocks with typical errors of less than 20 milliseconds are provided by radio corrected quartz clocks using WWVB, MSF, DCF77, JJY, and RTZ -- all VLF radio time signals. Check out Low-frequency Radio Time Signals and other internet references. Compared to other time-signal transmissions in higher bands (WWV, GPS, etc.) long-wave signals have a number of advantages: They can go around obstacles such as mountains or buildings. Since no line-of-sight is necessary between the transmitter and receiver, a single very powerful station can cover a huge geographic area. Long-wave signals even penetrate the walls of most buildings quite well. Propagation happens mostly in the form of a ground wave, such that transmission delay is less affected by the variability of the ionosphere. However, they are susceptible to local radio interference, particularly from CRT-type computer monitors! You need a gap larger than 6 feet. The transmitters may temporarily cease operation if a local thunderstorm threatens the very large aerial system. The clocks may operate OK at night in 'fringe reception' areas over 2000 km from the transmitter. 3,000 km is about the far limit for night time ionospheric reception. For the WWVB reception areas and times in North America, see WWVB. You can also buy the 60 KHz aerial and radio modules. Decoder modules should be available.

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