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WWVB field strength and readability for 2015-01-30
(as received outdoors in Santa Clara , California)

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Data Points Average
Readability Index
143 3.57






Legend
Dark PathThe period when it is dark at both the transmitting site in Ft. Collins, Colorado, and the receiving site. The 60 kHz WWVB signal is strongest during the dark path hours, so the period between the vertical green lines on the graph is the best time for reception.
Top Graph The top graph shows the measured field strength of WWVB at the monitoring site. The unit is microvolts per meter.
Bottom GraphThe bottom graph shows the readability of the received signal. The WWVB time code is sent at the very slow rate of 1 bit per second. A complete time code contains 60 bits of information and requires a full minute to be sent. In order for a radio controlled clock (RCC) to to synchronize, it must be able to successfully read and decode time code bits for at least a full minute, and many products require at least two complete time codes to be read before they display the received time. Fluctuations in the signal strength, even if the signal is strong, might make it impossible for a RCC to successfully decode the time. Keep in mind that not all RCCs are created equal, some employ advanced digital signal processing techniques that will allow them to synchronize under conditions where other products will fail.

The readability rating displayed in this column was designed to estimate whether or not a RCC will be able to synchronize. Keep in mind that these ratings only apply if your RCC is located in the same region of the country as the signal strength meter. The current signal readability rating can have one of four different values:

  • 4 - Excellent - Nearly all properly functioning RCCs should be able to synchronize under these conditions.
  • 3 - Very Good - Most RCCs will be able to synchronize under these conditions.
  • 2 - Intermittent - The conditions are not optimal, but a well designed RCC should still be able to synchronize.
  • 1 - Unreadable - It is highly unlikely that a RCC will be able to synchronize right now, but conditions should improve later.

    Most products only attempt to synchronize at night when the readability conditions are generally Excellent or Very Good in most parts of the continental United States. If you cannot get your RCC to work during the daytime hours, it will still probably synchronize if you let it run overnight.


  • Questions? See our information page on radio-controlled clocks.   Contact email: novick@nist.gov