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Tuesday Evening
05 March 2002


Subject: Time Synchronization Via Radio
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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
                             information.

                             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
                             submerged).

                             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.

'More'
                             Check on-line (search the Web) or look in the
                             'World Radio/TV Handbook' for lists of other
                             time stations.
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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 !

Paul

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