NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Atomic Clocks
From: Lu Abel
Date: 2012 Mar 23, 09:00 -0700
From: Lu Abel
Date: 2012 Mar 23, 09:00 -0700
To the best of my knowledge, WWVB broadcasts the complete time - ie, hours and minutes as well as seconds. I have handled atomic clocks straight out of the box where I inserted battery and then waited for the clock to set itself to the correct time (I did not set it to approximately the correct time, just put a battery in it and let it try to set itself). In no instance did the clock sync itself to the incorrect hour or minute.
I personally have a digital atomic clock that seems to be spot-on all day, every day. But I have also had experience with a
dozen Chinese-manufactured wall clocks where they took days to set themselves correctly (and a couple never did). I attribute this to cheap, poorly designed receivers that lack the sensitivity to pick up the signal from WWVB. Most of these clocks set themselves after being left outdoors (signals don't have to go through buildings) at night (signals tend to be stronger and propagate farther). This was in the San Francisco area, so about 1000 miles from WWVB's transmitter in Fort Collins, Colorado. If these junky clocks could not set themselves in San Francisco, I wonder how they work in more distant Chicago or New York.
Bottom line: Just because a timepiece is labeled "atomic clock" does not mean that it will successfully, correctly, and reliably receive
the synchronizing signal from WWVB.
From: David Fleming <d.l.fleming.1@gmail.com>
To: NavList@fer3.com
Sent: Friday, March 23, 2012 7:20 AM
Subject: [NavList] Re: Extremely poor conditions??Atomic Clocks
Given the expected rate error in a quartz clock and a premium for memory in a updateable atomic clock it is reasonable to assume only a seconds error for such a clock. Ie a programmer might make such an assumption. So If a clock had not been updated for say half a year and then made contact with the WWV it could have the seconds right but be off by a minute. But is it likely that the clock wasnt updated for such a long time? No.Also a one minute time error would show a trending altitude error as the sun follows a parabolic path in the sky. How noticeable that would be I haven't evaluated?On the other hand let me quote Bowditch, 1984 1605. Dip:4th paragraphThe values given in the table are satisfactory for practical navigation. An investigation by Carnegie Institution of Washington showed that of 5000 observations at sea, value differed from tabulated value by more than 2.5', except for one difference of 10.6'. Extreme values of more than 30' have been reported and even values of several degrees have been encountered in polar regions. Greatest variations from tabulated values can be expected in calm weather, with large differeences between sea and air temperatures, particularly if mirages are present. etc.
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