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A use for that old GPS...

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I was setting up network time sync software (NTP) on all the computers in my office so that they all stay consistent (important when you have shared files in use across a network) and I read that there are drivers for generic NMEA GPS units so that you can use the recieved GPS clock signal as your master clock.

Since I have a spare GPS, I am setting this up. I hooked up my old Magellan MAP 410 to a 12V supply on the PC by hacking up a spare power/data cable. I'm running the serial data into a port on a PC running Linux which will serve as the master time server. Since the MAP410 has a detachable antenna, I suction-cupped it to the window of my office.

So far so good.

My question is, since this will be running and collecting data over weeks and weeks, is there any useful/interesting data I can gather while I'm at it? I'm assuming that I could log the current calculated position, ephemeris, and signal strengths. Will odd changes in the signals help me detect incoming storms or anything like that? icon_smile.gif

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I thought the clock in the gps unit was set by the user...does it really recieve the time fron the satellites?! I have a Magellan 320.


The reason I thought it was user-set is I drove to a different time zone and the time didn't change. The gps should know what time zone I'm in and correct the time shouldn't it?



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Yeah, but I had a strange occurance with my merigold. It was like 2+ min behind (even after letting it get a fix, the unit still place me in the right area). I determined it was wrong by comparing it to a 315, a computers clock after I synced to the internet, the time from the satellite televison reciever, local televsion, and a digital phone. All of these usually desplay the same time. After I did a full reset it matched up pretty well with the 315 (the meridan has always been a few seconds behind).


I should mention that the unit was wrong for several days, I waited to reset till I found the 315 to make sure.


Wyatt W.


The probability of someone watching you is directly proportional to the stupidity of your actions.

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Originally posted by Martín:

Try this site and you should have the most accurate clock on earth.





The caveat on that site seems to say otherwise:

"This web site is intended as a time-of-day service only. It should not be used to measure frequency or time interval, nor should it be used to establish traceability to NIST or the USNO."


OTOH, when your GPS rcvr. is determining your position to an accuracy of about 30', it is also necessarily determining the GPS system time to a corresponding accuracy, which, at the speed of light, amounts to about 30 nanoseconds (i.e. billionths of a second). Of course the processor then takes its time actually updating the display and outputting any message, so the actual displayed time can be off by up to a second. Many of the board-level GPS rcvrs. have a timing output accurate to a microsecond.

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