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    Re: GPS shortcomings.
    From: Brooke Clarke
    Date: 2005 Jun 8, 18:51 -0700

    Hi Courtney:
    
    On the contrary, they will continue to work as they did, maybe better
    performance because of the improvements in the antennas, transmitters
    and the reference timing sources.
    
    But remember that LORAN-C was originally designed for coastal navigation
    and now the focus is on blind aircraft landing.  So the coverage area
    does not extend too far from any coast.  Global coverage map:
    http://www.locusinc.com/images/MegapulseMap1.gif
    
    But I expect the coverage area to increase, especially near major airports.
    
    I have a number of timing LORAN-C receivers and they are almost as good
    as GPS, see:  http://www.pacificsites.com/~brooke/A2100F.shtml
    
    Have Fun,
    
    Brooke Clarke, N6GCE
    
    
    
    Courtney Thomas wrote:
    
    > 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
    >>>
    >>>
    >>>
    >
    >
    >
    >
    
    
    

       
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