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    Re: Choice of timepiece
    From: Douglas Denny
    Date: 2009 Nov 13, 11:21 -0800

    John,
    
    Yes it is extremely odd that any electronics designer worth his/her salt 
    should allow such gross error in the display of GPS time signals,  when a 
    simple software adjustment could have made each (next) display update coupled 
    to the GPS second pulses which are accurate to practically atomic time.
    
    In fact it is not just odd it is bizarre.  I fail to understand why such a 
    gross blunder has occurred in various GPS equipments.
    Is it lack of cooperation between electronics engineers who deal with the nano 
    second accuracy pulses in the receiver/decode hardware circuitry and the 
    software designers who punch in the codes for how the on-board microcomputer 
    manipulates the numbers?  It's a mystery to me.
    
    The GPS satellites each have I think it is four atomic clocks on board, and 
    are used for continuous world-wide atomic time transfers/comparisons between 
    primary timekeeping standards bureaux, at Teddington (London); WWV at Boulder 
    Colarado; Paris and elsewhere.
    
    The GPS satellites do the same job that George Biddel Airy had performed in 
    about 1850 by sending thirty chronometers from Greenwich to Valentia in SW 
    Ireland twenty two times backwards and forwards to compare accurately the 
    longitude between the two, and to synchronise time measurement between the 
    two  observatories very accurately.
    (G. Airy who is responsible for the transit instrument at Greenwich which is 
    still the official world's Prime Meridian source - though adjustments to 
    Dynamical and GPS time put the modern meridian about 150 Metres to the East).
    
    ---------
    60 KHz signals are 'long wave' and are attenuated greatly over relatively 
    short distances (say a few hundred miles), so are only considered a 
    relatively small area service.  There is a 60KHz station in the NW of England 
    at the old Navy submarine VLF station at Anthorn for standard time signals; 
    (it used to be at Rugby).  This service is only considered useful for 
    coverage for the UK - i.e.  about say 400 miles North and South of the 
    station.
    
    5 MHz and 10 MHz are the best for long distance transmissions, with various 
    stations all around the world giving global coverage.
    --------
    Re:  NIST (or other) timesignals over the internet:
    
    I would NOT expect any website time standard to be more accurate than a couple 
    of seconds or even worse - as received.  If 0.2 seconds is quoted, I would  
    expect this perhaps be an average time delay expected for most of the time at 
    most places; but digital transmission paths vary for the internet. I would 
    not trust it for any kind of accuracy and certainly not being less than a 
    second.   If you use the 'ping' facility on an internet address you get all 
    sorts of return times.
    
    It might well be sent out as accurately as you like, but the digital 
    transmission paths from node to node can be varied and long and even delayed 
    whilst digital packets are waiting in a queue in the system.
    
    That is why when I used to listen to the 'Proms' (for Americans: a well known 
    music concert series from the Albert Hall in London sponsored by the BBC) on 
    my VHF radio, and watched the visual programme on digital TV there was a 
    difference of a couple of seconds between the VHF radio (instantaneous) and 
    the TV picture (two or more) seconds slow with the digital processing going 
    on.  I switched the TV off preferring the better quality of the radio sound.  
    Impossible to watch the TV and hear with the radio as the violins were being 
    bowed out of synch horribly. It's actually distressing to the brain to try to 
    watch.
    
    If you want accuracy for tie pips get the short wave receiver out.
    
    Regards,
    
    Douglas Denny.
    
    ==============
    Original Post:-
    
    Douglas,
    
    Well' I'll be darned.  I had no idea that the GPS receiver display
    could be off by seconds.  I naturally thought that, with atomic clocks
    onboard the satellites, the receivers would be displaying atomic-clock
    accuracy.  Thanks for setting me straight.  Actually, I have been
    checking my Timex against a small WWVB clock which receives 60Khz time
    signals from near Fort Collins, Colorado.  Does anyone know how this
    60Khz signal strength is world wide??
    
    There's also the NIST website at  http://nist.time.gov/timezone.cgi?Central/d/-6/java
    which claims 0.2 second accuracy.  Is that accuracy statement
    reliable??
    
    John
    
    
    
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