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Re: Date/Time accuracy (was Re: First TOM1 image under Rob's Software)
You are right. These source are better used as frequency
standrads.
Do any of the low cost comsummer GPSes offer the
pulse per second output? The two units that I own only send out
NMEA data sreams which are really just 1200 baud serial
ASCII text with <cr><lf> end of line convention.
--- James Hannon <jmhannon@fmtcs.com> wrote:
> Many GPS receivers have a 1 pulse per second output that is aligned
> with time to a few nanoseconds. by using this and the once per second
> NMEA data you can get very accurate time.
>
> All of the WWV clocks that I know of use the 60KHz WWV signal which
> is mostly ground wave so it does not have as much variation in time
> as the HF WWV signals.
>
> Jim Hannon
>
>
> ---------- Original Message ----------------------------------
> From: Chris Albertson <chrisalbertson90278@yahoo.com>
> Date: Wed, 16 Feb 2005 13:26:39 -0800 (PST)
>
> >
> >I think NTP is about 100 times more acurate then needed for TASS
> >but it's free and easy to set up.
> >At the level of resolution that us humans can notice "anything
> >works". Noticing to less than 1/10th second is hard.
> >
> >But if we are talking microseconds then even GPS has problems
> >because of the unpredictable propogation speed through the
> ionosphere.
> >The millitary grade GPS signal uses two frequencies so that the
> >differences in propogation speeds (which are frequency dependent)
> >tells the reciever enough about the real-time ionosphere that the
> >reciever can correct out the effects. Effects are on the order
> >of a few meters over "C".
> >
> >The bigger prolem with GPS, at the consummer level, is the update
> >rate of the LCD display and delay through the NMEA data port.
> >
> >WWV radio is in the HF frequency range and unless you live very
> close
> >to the transmitter comes to you after bounceing offone of the
> >ionoshpere layers. The layers are not at constanthight so the path
> >lenght varies durring the day.
> >>
> >
> >
> >=====
> >Chris Albertson
> > Home: 310-376-1029 chrisalbertson90278@yahoo.com
> > Cell: 310-990-7550
> > Office: 310-336-5189 Christopher.J.Albertson@aero.org
> > KG6OMK
> >
> >
>
>
> --
> Jim Hannon
> http://www.fmtcs.com/web/jmhannon/
> 42,11.90N,91,39.26W
> WB0TXL
> --
>
=====
Chris Albertson
Home: 310-376-1029 chrisalbertson90278@yahoo.com
Cell: 310-990-7550
Office: 310-336-5189 Christopher.J.Albertson@aero.org
KG6OMK
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