PSN-L Email List Message

Subject: Re: Precise Frequencies derived from GPS
From: Bob Smith bobsmith5@........
Date: Mon, 08 May 2000 10:19:54 -0400

Hello All --

I have been a lurker here for several weeks because
seismology is a latent interest.

As I am not a currently active seismologist so I am not sure
what sort of timing requirements are needed to correlate
independent observations.  My gut feel is that
something in the one millisecond region is adequate.

Anyway, Mark's pointer to the work by Brooks Shera is very
relevant.  His GPS derived, phase locked oscillator control
will certainly lead to an excellent frequency reference, and
thus, a very stable time base.

Perhaps of more interest to the PSN may be the work in
direct GPS timing lead by Dr. Thomas A. Clark of the Goddard
Space Flight Center and well known radio amateur (W3IWI)  in
the development of low cost GPS timing references.

It is my understanding that using GPS as a time reference,
you can achieve sub-microsecond clock accuracy's with
relative ease.

For those interested in following these interesting
developments I recommend that they explore the TAPR (Tuscon
Amateur Packet Research organization) web site at

There you will find information on the TAC-2 (Totally
Accurate Clock) developed by Dr. Clark and the TAC-32
companion PC software by another dedicated radio amateur
that derives a very stable time base directly from GPS
signals.  Interested parties should also follow links to the
TAPR SIGs (Special Interest Groups) and join the TACGPS
email list.

Also by linking to you will reach the
NIST time standards home page with has many interesting
links to information on precision timekeeping and frequency

	Best wishes, Bob Smith

Mark Robinson wrote:
> I thought some members of the PSN community may be interested in this page :
> It describes a unit which uses a phase locked loop locked to the GPS clock
> to give accuracies measured in parts in 10^12.
> My mind is unable to recall this being posted here before.
> regards all
> Mark
> Mark G Robinson    |    ZL2TOD    |   other@...............
> Box 8770,            Auckland 1035,             New Zealand
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---------  Avoid computer viruses  --  Practice safe hex 
 * * Specializing in small, cost effective embedded control
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Robert L. (Bob) Smith			Smith Machine Works, Inc.
internet   bobsmith5@.............. Lumlay Road
landline   804/745-1065	                Richmond, Virginia

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