NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: GPS shortcomings.
From: Courtney Thomas
Date: 2005 Jun 8, 21:28 -0500
From: Courtney Thomas
Date: 2005 Jun 8, 21:28 -0500
Does this mean our old Loran receivers are soon worthless, or still usable just not as accurate, or what ? Thank you, Courtney On Wed, 2005-06-08 at 16:19, Brooke Clarke wrote: > Hi Carl: > > The current LORAN-C system is made up of chains of stations, one master > and a hand full of slaves. Now the slaves listen for the master pulse > and after a wait send their pulse. In the not too distant future all > stations will just transmit based on a collection of Cesium clocks. > > The result will be a more accurate fix. > > The older LORAN-C receivers could needed to be programmed for the Group > Repetition Interval (GRI) of the nearest chain. The new generation > receivers are, to borrow a GPS term, "All In View". These receivers > know about all the world's stations and use Digital Signal Processing > technology to receive all the stations at the same time. > > It was not only the events on 9/11 but also the realization that it's so > easy to jam GPS and European and Russian counterparts that kept LORAN-C > alive. > > The U.S. has turned off Selective Availability which makes a GPS fix > more accurate for civilian users, but to counter this the military is > developing jamming technology and from time to time tests it. If you > happen to be in a test area you position will be either wrong or non > existent. > > Have Fun, > > Brooke Clarke, N6GCE > -- > w/Java http://www.PRC68.com > w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml > http://www.precisionclock.com > > > > Carl Herzog wrote: > > Lu Abel wrote: > > > >> Two or three years > >> ago the US Coast Guard was trying to accelerate their schedule for > >> shutting down Loran C. Now it looks like they and the US Department of > >> Transportation (which includes the US's Federal Aviation Administration) > >> are concerned about possible problems with GPS in navigation > >> applications (such as aircraft routing or precision harbor approaches) > >> that require hyper-reliability and appear to be considering an enhanced > >> Loran as a backup system. > > > > > > As of 1992, plans were in place to eliminate LORAN by 2015. By 1994, the > > termination date had been bumped up to the year 2000. Opposition by > > LORAN users, largely lead by general aviation interests, caused another > > review of the need for the system. > > > > At the same time, in an unrelated effort, the Volpe National > > Transportation Systems Center, a division of the U.S. Dept. of > > Transportation, was studying the vulnerabilities of the GPS system. They > > released their resulting paper on September 10, 2001. This report is > > available as a pdf online: > > > > http://www.navcen.uscg.gov/archive/2001/Oct/FinalReport-v4.6.pdf > > > > Needless to say, the events the next day gave the report a higher > > profile than it may have otherwise had. > > > > It was shortly after that the department began looking at refurbishing > > the existing LORAN infrastructure to backup GPS. Upgrades to the LORAN > > infrastructure in the U.S. are already well underway. This spring the > > Coast Guard upgraded all the transmitters and new timing and frequency > > equipment is being installed this summer. > > > > Studies are still underway to determine whether an enhanced LORAN system > > can completely meet standards for accuracy and other characteristics > > that would be required for it to serve as a backup to GPS in aviation > > and harbor approach navigation. So far the results look promising, but > > it may be a few more years before you start seeing integrated GPS/LORAN > > receivers for sale at your local marine supply store. > > > > Carl > > > > > >