Re: WWV DST

[rrennard]

Mark -

I think you need to find the NMEA 0183 specification for $GPxxx strings.  They are a lot easier to write a simple program to read than bit-banging to extract a DST bit from a binary stream.  

How did knowing the DST bit help anybody who lived in Indiana before the law change last weekend?  At best, it was a warning to apply local knowledge.

Read the other threads about the variation in the iono layer height impacting WWVB timing, and you'll have to agree that WWVB clocks are at least good to a minute, while GPS is good to better than a microsecond.   The earth radius is about 6380 kilo-KM, so if you can get GPS synched up, you have time to about 20 ms - add a position solution, and you have time to about 0.1 microsecond.  There must be a reason why the military uses GPS for time dissemination.   http://tycho.usno.navy.mil/gpstt.html

N7WY

---- Mark Bayern <[hidden email]> wrote:

> Thanks for the reference. However, the idea that this system is
> 'superior' would depend upon why one is looking for a time reference.
> If all you want is a relatively high accuracy clock the WWV signal is
> superior IMO. It certainly is easier to decode! As an added benefit it
> includes the DST bit -- you never know when the govt will decide to
> change the DST rules.
>
> If you need to know where you are and have a clear view of the sky
> your system works well.  (As long as I don't have to code the
> algorithms.)
>
> Mark
>
> On 4/3/06, [hidden email] <[hidden email]> wrote:
> > Mark - you are correct... I am just to used to working with the superior system described at
> >
> > http://www.navcen.uscg.gov/pubs/gps/sigspec/gpssps1.pdf
> >
> > that is only good to about 100 nanoseconds anywhere on the planet, but it has no clue about DST.   The starting and ending dates for DST are easy to determine if you can figure out which day of the month it is, and what day of the week it is.
> >
> > N7WY
> >

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[Stuart Rohre]

Actually, WWV and WWVB are not worldwide in range.  Military uses a system
that is space based so they can see 12 satellites for a "fix" from anywhere
on the globe they may need position.

But, there are effects to GPS signals if you are not using a 12 satellite
solution, and thus, GPS quality at your receiver may depend on a number of
factors.

Higher quality GPS solutions come from the differential methods pioneered by
our university laboratory.  I am proud of my friends that developed the
method to measure a bridge moving in the wind, for example.

Stuart
K5KVH



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