From: default@defaulter.net   
      
   On Fri, 13 Jun 2008 22:46:40 -0700, "caveat"    
   wrote:   
      
   >   
   >"default"  wrote in message   
   >news:1213400540_8606@isp.n...   
   >>   
   >> On Thu, 12 Jun 2008 13:07:45 -0700, GeoSound    
   >> wrote:   
   >>   
   >>>Am thinking about building an electronic sextant that would provide near   
   >>>centimeter accuracy.  This would mean a degree should be partitioned to   
   >>>about 400,000 steps.  Was considering using a pot and 5v to feed an A/D   
   >>>but on reflection think that a single turn pot would not be clean enough   
   >>>for that many steps.  Would someone confirm this for me.  Use of a   
   >>>multi-turn pot requires gears which would be too expensive due to their   
   >>>very critical meshing needed.  Thanx, Ron   
   >>   
   >> Another idea - a old time variable capacitor.  The position of the   
   >> knob is directly proportional to the capacity   
   >   
   >Not always true.   
   >   
   > - and that can easily be   
   >> resolved into a lot of counts by counting an  oscillator's frequency.   
   >>   
   >> Look into VFO ("variable frequency oscillator") amateur radio   
   >> operators use them in home built receivers - and they have various   
   >> schemes for digitizing the outputs.   
   >> --   
   >   
   >The problem with a variable capacitor is that it can "drift" with   
   >temperature and humidity changes.   
   >   
   >Many years ago,1990's, I worked for a company that produced LORAN-C   
   >receivers and they could, in the experimental models for the military,   
   >locate you to within a foot or less if they could tune in 20 to 30 towers   
   >but I have never heard of anything available to the public that can locate   
   >you to within a centimeter. At that, they used state-of-the-art Cesium clock   
   >generators and racks of clasified high-tech stuff. But, then I was never   
   >allowed in to the section of the building where the government security   
   >cleared Ph D's worked.   
   >   
   >I don't believe that you can create a device that will, reliably, position   
   >you to within a cm or two from simple publically available components, be it   
   >GPS, LORAN or Sextant.   
   >   
   I'm not really sure what this guy wants . . .   
      
   I don't think anyone expects centimeter accuracy on earth with any   
   global location scheme, least of all a sextant.  I'm assuming he just   
   wants to read a sextant to a high degree of resolution, not   
   necessarily fix his position to a centimeter with one.   
      
   And he's talking about the expense . . .   
      
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