Next message: Brooke Clarke: "Re: GPS shortcomings."
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
> >
> >
> >
