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 http://www.tapr.org 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 http://www.time.gov you will reach the NIST time standards home page with has many interesting links to information on precision timekeeping and frequency standards. Best wishes, Bob Smith Mark Robinson wrote: > > I thought some members of the PSN community may be interested in this page : > > http://www.rt66.com/~shera/ > > 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 > Phone +64-9-846-3296, +64-9-817-4577 Pager +64-26-351-2770 > ----------------------------------------------------------- > 04 May 1863 Taranaki Maori retaliate against renewed european settlement and > ambush a party of soldiers returning from Tataraimara > 04 May 1891 Auther Conan-Doyle's character Sherlock Holmes died. > 04 May 1953 Ernest Hemingway wins the Pulitzer Prize for "The Old Man and > the > Sea", William Inge wins for his play "The Picnic". > 04 May 1968 The Big Mac is invented by a McDonald's Manager in Philadelphia. > 04 May 1969 Radio Bosom, The Auckland University Student's Association Radio > Station officially starts broadcasting. > 04 May 1970 Four student vietnam war protestors are shot and killed at Kent > State University. > 04 May 1991 President Bush is admitted to hospital with arrythmia. > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. -- --------- Avoid computer viruses -- Practice safe hex ------------- * * Specializing in small, cost effective embedded control systems * * Robert L. (Bob) Smith Smith Machine Works, Inc. internet bobsmith5@.............. Lumlay Road landline 804/745-1065 Richmond, Virginia 23236+1004 __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>