NIST Time Signals

• What phone numbers do I dial to listen to NIST time?
• Can I buy a clock or wristwatch that receives NIST time?
• Can I synchronize my computer clock to NIST time?

Radio stations WWV and WWVH

• What frequencies do WWV and WWVH use to broadcast their signals?
• When I listen to WWV or WWVH, how accurate is the time?
• What other information is broadcast on WWV and WWVH besides the time announcements?
• What do the call letters stand for?
• How do I convert the time announced on WWV or WWVH to my local time?
• Is it possible to tour the WWV facilities in Colorado or the WWVH facilities in Hawaii?
• Why are both male and female voices used for the time announcements?

Radio stations WWVB

• My WWVB radio controlled clock isn't working properly, what should I do?

What phone numbers do I dial to listen to NIST time?

There are two phone numbers that allow you to listen to NIST time. To hear a simulcast of the WWV shortwave broadcast, call (303) 499-7111. This is not a toll-free call, except in the local Boulder/Denver, Colorado area. To hear a simulcast of the WWVH time announcements from Hawaii, call (808) 335-4363.

Can I buy a clock or wristwatch that receives NIST time?

Yes. The 50 kW signal from NIST Radio Station WWVB located in Fort Collins, Colorado is the synchronization source for a growing market of clock and wristwatches. These products work in the continental United States and display NIST time, all the time. See our links to receiver manufacturers for some potential sources.

Can I synchronize my computer clock to NIST time?

Yes. You can synchronize your computer clock to NIST using either an Internet or a dial-up service, and some simple client software.

What frequencies do WWV and WWVH use?

WWV broadcasts on 2.5, 5, 10, 15, and 20 MHz from Fort Collins, Colorado. WWVH broadcasts on 2.5, 5, 10, and 15 MHz from Kauai, Hawaii. Both stations continuously broadcast a timing signal - 24 hours per day, 7 days per week to listeners all over the world.

All broadcast frequencies used by WWV and WWVH are in the high frequency (HF) part of the radio spectrum that extends from 3 to 30 MHz. This part of the spectrum is commonly referred to as "shortwave". General coverage shortwave receivers typically receive all frequencies from 530 kHz (the beginning of the AM broadcast band) to 30 MHz, and are capable of receiving WWV and WWVH on all of the available frequencies.

Multiple frequencies are used because shortwave propagation varies with many factors, including time of year, time of day, geographical location, solar and geomagnetic activity, weather conditions, and antenna type and configuration. In general, the lower frequencies of 2.5 and 5 MHz are best during nighttime hours, the higher frequencies of 15 and 20 MHz are better during daytime hours, and 5 and 10 MHz are probably the best compromises overall. The 5, 10, and 15 MHz transmissions are at higher power than the other frequencies.

When I listen to WWV or WWVH, how accurate is the time?

The time is kept to within less than 1 microsecond of Coordinated Universal Time (UTC) at the transmitter site, but the signal is delayed as it travels from the radio station to your location. This delay increases the further you are from the station, and also changes at various times during the day if the signal is bouncing between the earth and the ionosphere. However, for most users in the United States, the received accuracy should be less than 10 milliseconds (1/100 of a second).

If you listen to signals by telephone, the delays will probably be larger, but the time should still be accurate to less than 40 milliseconds.

What other information is broadcast on WWV and WWVH?

WWV and WWVH broadcast much more than just the time. Please visit the station home pages to read about the information transmitted by WWV and WWVH.

What do the call letters stand for?

Nothing. They are merely a unique combination of letters, just as for a commercial radio or TV station, that meet certain requirements as spelled out in the International Telecommunication Union's Radio Regulations (for example, call letters for U.S. radio and TV stations begin with a "W" or a "K").

How do I convert WWV or WWVH announcements to my local time?

The time announced on WWV and WWVH is Coordinated Universal Time or UTC. UTC is a 24-hour time system, similar to "military" time. Thus, instead of AM and PM hours, its hours are numbered beginning with 00 at midnight, through 12 for noon, and ending just after 23:59:59 with 00 hours of the next day. The announced hour refers to time at the 0 or Greenwich meridian. Therefore, to obtain your local time, subtract a certain number of hours from what you hear, depending upon the number of time zones between your location and Greenwich, England.

For example, suppose you are in the Eastern time zone of the U.S. and you hear WWV announce the next minute as being: "22 hours, 10 minutes, Coordinated Universal Time." To refer this time to Eastern Standard Time, you would first need to subtract 5 hours from the announced time since the Eastern time zone is 5 time zones away from the Greenwich meridian. This makes your local time 17 hours, 10 minutes. Next, since the hour is greater than 12, subtract 12 hours to get 5:10 p.m. If your locality is currently on Daylight Saving Time, subtract 4 hours from the announced hour instead of 5 hours, since UTC does not change with respect to Daylight Saving Time. In this case your local time would be 6:10 p.m.

Is it possible to tour the WWV/WWVB facilities in Colorado or the WWVH facilities in Hawaii?

Unfortunately, no. The small size of the staff at each station makes it impossible to provide tours. However, you can view images of the facilities online.

Why are both male and female voices used for the time announcements?

WWV uses a male voice and WWVH uses a female voice. The antenna system of WWVH in Hawaii is especially designed to minimize radiation back toward the U.S. mainland in order to prevent mutual interference with WWV on the same frequencies. However, interference sometimes occurs under favorable propagation conditions. Often in the nighttime hours, it is possible to hear both stations simultaneously, but the two voices never speak at the same time.

My WWVB radio controlled clock isn't working properly, what should I do?

Since we receive many inquiries, we created a special page to answer questions about WWVB radio controlled clocks.