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