WWVB synchronization

Discussion in 'General Electronics Chat' started by John P, Jan 25, 2013.

  1. John P

    Thread Starter AAC Fanatic!

    Oct 14, 2008
    I'm sure most people here know what WWVB is:

    I just bought an indoor/outdoor thermometer which has a clock display, which the instructions said would synchronize to the WWVB time signal, but "Several hours may be required". In fact, when I put batteries in the unit, I didn't see it show the right time until the next morning. I'm puzzled by this, because I thought the time signal was much more frequent, and when I looked it up I found out that indeed, the signal repeats every minute. So what happened overnight? I'm thinking that maybe at my location (Massachusetts, and the signal comes from Colorado) the signal is so weak that maybe the receiver has to wait for the most favorable time of day to receive it. Could it be that if the location were really bad, it would never lock at all?
  2. bertus


    Apr 5, 2008
  3. davebee

    Well-Known Member

    Oct 22, 2008
    I've got a WWVB clock, in California, and it also needs to run overnight before it will synchronize. I've heard that a long time correctness verification process is written into the radio decoding algorithm, to be sure the time is being decoded properly, but I have no way to know for sure.

    Have you seen these signal strength maps? Massachusetts will have quite a large variation in signal strength over the day.

  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Here is a long quote from a guy who built a WWVB-synced clock. He explains why it takes so long to sync up.
    Be sure to read the entire article. It is very informative.
  5. SPQR


    Nov 4, 2011
    I love these clocks.
    When I lived in LA, there was no problem.
    I moved outside of LA and now the signal is horrible, and I can't use them.
  6. bretm


    Feb 6, 2012
    I built one of these using the CMAX module and saw the same thing--terrible reception during the day, clean signal at night.

    It's actually a sorry tale. I built a New Years count-down clock that counted down the number of seconds until New Years. It started from 31 million+ on January 1st and counted all the way to zero, so I wanted it to be very accurate to avoid countdown glitches.

    I got it working pretty well, then shelved it for most of the year. I turned it on again on December 29th and it resumed its countdown that night. The cat jumped onto my workbench and knocked the clock off and the CMAX module broke! I never did find out if the software did the right thing at zero.
  7. crutschow


    Mar 14, 2008
    I believe many of the clocks are designed to turn on the WWVB receiver to check the signal only once a day, late at night. That's both to try to receive the signal when it has the best signal/noise ratio and also to minimize the extra battery power required for the receiver.

    I have one with analog hands. Initially it resets all three hands to the 12 position. Then it's interesting to see the hands rapidly move to the correct time after it picks up the signal. A few times a year there's apparently a glitch in receiving the time and the time will be significantly off in the morning.
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    It could also just be that the thermometer only updates or wakes that part up every "X" hours to prolong battery life.
  9. Papabravo


    Feb 24, 2006
    Propagation on the HF bands from 3-30 MHz is highly variable on a daily and seasonal basis. To alleviate this problem somewhat there are standard time signals at 2.5, 5.0, 10.0, 15.0 and 20.0 MHz. Generally speaking the higher frequency signals may work better in the daylight hours while the lower frequency signals tend to be better at night and in the early morning hours.

    Also recognize that for those frequencies any short antenna is likely to provide really poor performance. The 20.0 MHz has a wavelength of just a bit over 15 meters, while the 2.5 MHz. signal is about 150 meters. As any ham will tell you a good antenna at those frequencies can be a challenge to build.

  10. crutschow


    Mar 14, 2008
    The WWVB broadcast frequency is 60kHz which propagates well over long distances with comparatively low power. Obviously at such a low frequency the antenna cannot be anywhere near a quarter wavelength so compact ferrite core antennas or some type of resonant loop is typically used.
  11. Papabravo


    Feb 24, 2006
    Right you are. I was confusing WWVB with WWVH(Hawaii) thinking the "B" was for Boulder, CO. It is actually in Fort Collins, CO

  12. nsaspook

    AAC Fanatic!

    Aug 27, 2009