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    Time Synchronization Via Radio
    From: Paul N. Nix
    Date: 2002 Mar 5, 21:13 -0600

    Tuesday Evening
    05 March 2002
    Subject: Time Synchronization Via Radio
    This information is probably well known by most but perhaps not to all.
    Time Sources via radio from U.S. Govt. sources;
      60 kHz VLF (Very Low Frequency)
                                 Radio Station WWVB in Fort Collins, Colorado.
                                 This is typically what the various radio-controlled
                                 clocks of the last few years synchronize against.
                                 WWVB does not send out a voice signal but rather
                                 a slow data signal that provides time and other
                                 At 60 kHz WWVB propagates via 'ground wave' as
                                 opposed to reflecting off the ionosphere like
                                 short wave stations do. Ground wave is dependent
                                 on the surface of the Earth's electrical
                                 properties and studies have been performed
                                 to ensure reasonable signal levels across the
                                 continental United States. If the signal makes
                                 it to salt water the distance travelled will
                                 be enhanced as salt water is an astonishingly
                                 good medium (low loss) compared to dry land and
                                 fresh water (that's why the Navy has to work so
                                 hard to maintain communications with submarines
                                 as they are shielded from most radio energy when
                                 Ground wave propagation is affected by daylight/
                                 night-time effects. The 'Oregon Scientific' radio
                                 controlled clocks (at least the two I use) 'listen'
                                 every 6 hours and always manage to synchronize at
                                 least in the hours between midnight and dawn.
       2.5, 5, 10, 15 & 20 MHz HF (High Frequencies - 'Shortwave')
                                 Radio Station WWV in Fort Collins, Colorado
                            and  Radio Station WWVH in Hawaii (except no 20 MHz)
                                 These stations transmit an AM signal providing
                                 voice announcements that can be received by
                                 any reasonable shortwave receiver. The time is
                                 announced every minute and it makes it quite
                                 easy to check timepieces. Although hard to hear
                                 there is also a low-level data modulation applied
                                 that has been used to synchronize clocks but they
                                 seem uncommon now that WWVB has been reworked to
                                 cover the continental U.S. more effectively.
                                 Due to the fact that HF stations propagate via the
                                 ionosphere reception can vary radically from daytime
                                 to night, sometimes even a few minutes can make a
                                 big difference. To use the HF services with a minimum
                                 of difficulty it helps to have a synthesized receiver
                                 with all the different frequencies pre-set so you
                                 can painlessly switch between them until you find a
                                 frequency that's making it to you with a decent signal.
                                 Here in the Dallas (Tx) area we sometimes hear a time
                                 station in Venezuela on the same frequencies as WWV
                                 when the ionosphere favors signals from South America.
                                 Changing to a lower frequency will usually then allow
                                 receiving WWV as (most of the time) a lower frequency
                                 will not propagate as far as a higher frequency (let's
                                 not confuse people with a discussion of 'LUF' & 'MUF').
    'Other' .... non-U.S. Gov't sources:
        ~3.3, ~7.335 and ~ 14.4 MHz HF
                                 Radio Station CHU in Canada.
                                 You'll need to look up CHU's exact frequencies but
                                 otherwise they're of the same utility as WWV. CHU
                                 provides announcements in English and French. Note
                                 that CHU transmits using Upper Sideband (USB) and
                                 so you'll need a USB capable receiver for CHU.
                                 Check on-line (search the Web) or look in the
                                 'World Radio/TV Handbook' for lists of other
                                 time stations.
    There are LOTS of ways to use radio to perform timechecks.
    Use what you're comfortable with; better yet have more than one method available
    (I have two radio controlled clocks that synchronize against WWVB and I have a
     shortwave receiver that I use to listen to the voice announcements from WWV).
    Cheers !
                                      - End -

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