It was in the month of May just several years back that Prez. Clinton ordered 'SA' (Selective Availabilty) turned off - could that be what you are making reference to? SA caused readings/the reported position to drift to and fro - it seemed to do it in a more or less sinusoidal way - both position (lat/long) and altitude varied. I *guess* this was done so that no hostile foreign power could target the front doors of Cheyene Mt. with an ICBM via the proper coordinates marking same. Since SA has been turned off - there isn't near as much 'drift' as before. But there still is some 'drift'. As it takes 24 some birds to cover the earth - I find it *very* difficult to believe that these birds were actually turned off. Although it is still possble - the entire GPS/NAVSTAR system could/can as any time be made 'unavailable' at the behest of those in charge in a moment with no notice whatsoever (perhaps when NORAD views ICBMs coming over the Pacific or over the N. pole they would 'turn down' GPS for a short period 'til the ICBMs terminate somewhere). Some of the better GPS OEM-class receivers will actually output the bird numbers used for fix/or currently in view as well as their 'signal stringth'. It is easy that way to observe and perform an audit verfying those birds that the NAVSTAR program office shows as 'active'. The GPS/NAVSTAR program office still maintains a web site where they post the health of the birds in service - years back this used to be available via a dial-up BBS system. My how times have changed ... Jim ----- Original Message ----- From: "Kathy Quinlan" To: Sent: Friday, August 31, 2001 7:30 PM Subject: Re: [EE]: - Botboard > Jim, > > All I can remember was an article stating that during the gulf war the > accuracy of the GPS system was increased dramatically, and after the war > finished, some of the satellites were turned off :o( > > The accuracy could have been ,10 mm not cm as it has been a while since > reading the article. > > > Regards, > > Kat. > > ____________________________________________________________________________ > The information contained in this email and any files transmitted with it > are confidential and intended solely for the use of the individual or entity > to whom they are addressed. If you have received this email in error please > promptly notify the sender by reply email and then delete the email and > destroy any printed copy. If you have received this email in error, you must > not disclose or use this information in any way. > ____________________________________________________________________________ > > > ----- Original Message ----- > From: "Jim" > To: > Sent: Friday, August 31, 2001 11:01 PM > Subject: Re: [EE]: - Botboard > > > > "I think when all the satellites are operational the > > accuracy is in the cm's (<10cm)" > > > > Do you have a source on that accuracy figure? > > > > Is that using what is called 'P code' - Precision code, > > using a 10.23 MHz chip rate and available -so far- only > > to the US Military versus 'C/A code' - (Course/Acquisition > > code - available for civil apps) which uses a 1.023 MHz > > chip rate? > > > > There are ways right now to gain increased accuracy - such > > as DGPS - differential GPS - simplified explanation: a technique > > wherein *the position error* in the GPS sugnal from the satellites > > in a given geographical area is noted and transmitted for use as a > > correction factor by user-segment GPS equipment. > > > > One could *also* implement one's own localized "GPS" > > system (as was done when test of the system was done at > > Yuma Az) during development testing. One could use the > > principles of the GPS system and implement a localized > > position determining system using unlicensed gear in the > > 900 MHz ISM-band ... perfect app for a PIC ... > > > > > > Jim (a veteran of GPS/HDUE (High Dynamic User Equipment) > > development at TI in the late seventies ...) > > > > > > ----- Original Message ----- > > From: "Kathy Quinlan" > > To: > > Sent: Friday, August 31, 2001 9:10 AM > > Subject: Re: [EE]: - Botboard > > > > > > > Start another war involving America, all the military satellites come > > online > > > and use GPS I think when all the satellites are operational the accuracy > > is > > > in the cm's (<10cm) > > > > > > Regards, > > > > > > Kat. > > > > > > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics