From: henry@spsystems.net   
      
   In article <1104968476.664619.36540@c13g2000cwb.googlegroups.com>,   
   thomsona@flash.net  wrote:   
   >> Civilian receivers have limits on speed and altitude to prevent   
   >> people from using them to make ICBM guidance systems, for example.   
   >   
   >True, but even in the mid-1990s, when a red team looked at this, it   
   >turned out that many GPS vendors implemented the limits in ways that   
   >were readily circumventable.  At least one, in Canada IIRC, just put   
   >the limitation in the display driver.   
      
   Unfortunately, there is more to building a satellite GPS receiver than   
   just taking the limits off.  Consumer receivers are unlikely to be able to   
   cope with the high Doppler shifts, rapid motion, and fast changes of   
   satellite visibility.   
      
   (And there are known problems with consumer receivers in high-vibration   
   environments, which don't matter to a satellite but are significant for   
   rocketry.  Things like crystal oscillators and SAW filters can malfunction   
   when vibration gets excessive.)   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
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