Re: Date/Time accuracy (was Re: First TOM1 image under Rob's Software)

[James Hannon <jmhannon@fmtcs.com>]

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
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