Miata Mailing List: February 1997, Message #109
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   From: (none)

Subject: Re: Inaccuracies of GPS 

   Date: (none)



In a message dated 97-02-02 02:12:14 EST, n6mod@amt.org (Aleksandr Milewski)

writes:



> 	The DoD has decided that it would be a Really Bad Idea to put up a

>  satellite navigation system that would provide highly accurate positition

>  data with an average, consumer reciever. So, they munge the data a little

>  bit on the signals that are easy to decode, and keep the good stuff for

>  themselves. However during the only war to take place since GPS has become

>  operational, SA was turned off so the US Military could use average,

>  consumer GPS units. :-\



I had dinner with an old friend the other night and he told me that he is now

working with some engineering company or other, on a contract/consulting

basis, which is working on a GPS problem the government is worried about.  It

seems that GPS is very vulnerable to jamming and that for a measly $500,000

or so of equipment, Saddam could have rendered the navigational capabilities

of the Desert Storm forces useless.



I found that quite interesting (he was talking about band widths and a whole

bunch of esoterica far beyond my comprension) and took the opportunity to ask

him about the accuracy of using GPS for speedometer calibration.  After some

thought and more talk of electronic and physics theory, again largely beyond

my understanding, said quite convincingly that he could see no reason to

preclude the use of GPS in checking your speedometer for accuracy.  In fact

he was quite excited to find an other use for his own GPS unit.



He also mentioned something about secret, changed-daily, algorithms (don't

test me on this) which military units have which allows them to be so much

more accurate than mere civilian models.  The government simply won't release

them to the manufactures of civilian models hence, the reduced accuracy.  



FWIW, I would be happy to forward any more detailed questions anyone might

have.



Ralph Alder

SoCal 90 Red A