March 13th 2017

When I established the forums in 2005 it was to offer a more richer web experience and greater functionality than the platform where we started this social adventure in 2003, Yahoo Groups. The forums were once a busy hive of activity and provided locals and visitors with a wealth of information just like the Geocaching Ireland Discussion Group on Facebook today.

It was a time where we didn't have the many social media platforms we have today, and it was a different time in terms of mobility and technology. There was no instant access to information, no Google Maps and a very limited base map on your GPSr. Mobile connectivity for me was a 9600bps Infrared connection from a Nokia to a laptop and in later times to a PDA using WAP.

As we moved into the social media era so did our forums users. Geocaching Ireland moved there too, and we have a thriving community on the Geocaching Ireland Discussion Group on Facebook. As a result, forum activity isn't what it used to be and I have taken the decision to disable new registrations to the forums and to make the forums read only so any information there can still be accessed.

The discussion hasn't ended, it has just moved. Join us on the Facebook Geocaching Ireland Discussion Group .

Donnacha

Stop The Clocks

Discuss Geocaching, Announce Your New Cache Here & Discuss Ideas For Caches

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Serapis
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Stop The Clocks

Post by Serapis » Mon Oct 22, 2012 3:33 pm

I have a bit of a 'techie' enquiry that somebody may be able to set straight. I found the X and O http://coord.info/GC3Y940 cache after the recent, (excellent) Kilkenny event. The cache is placed near a large sundial which set me thinking about the time (heavy stuff on Sunday morning after a few pints the night before).
The sundial is one of the most primitive if not the most primitive form of clock. Now the GPS receiver also displays the time and the question is – Is the time displayed by the receiver derived from the GPS signal and ultimately the atomic clocks on board the satellites? Or does the receiver generate it from its own internal circuit? If it is the former, which I think it is, it means that the most primitive and one of the most advanced time pieces are present by this cache.

Can anyone tell me for sure if the time displayed on our receivers is derived from the atomic clocks on the satellites or otherwise?

Thanks, Bren

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TXLiz
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Re: Stop The Clocks

Post by TXLiz » Mon Oct 22, 2012 5:23 pm

The Global Positioning System has a clever, effective solution to this problem. Every satellite contains an expensive atomic clock, but the receiver itself uses an ordinary quartz clock, which it constantly resets. In a nutshell, the receiver looks at incoming signals from four or more satellites and gauges its own inaccuracy. In other words, there is only one value for the "current time" that the receiver can use. The correct time value will cause all of the signals that the receiver is receiving to align at a single point in space. That time value is the time value held by the atomic clocks in all of the satellites. So the receiver sets its clock to that time value, and it then has the same time value that all the atomic clocks in all of the satellites have. The GPS receiver gets atomic clock accuracy "for free."

http://electronics.howstuffworks.com/ga ... l/gps3.htm
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THE_Chris
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Re: Stop The Clocks

Post by THE_Chris » Mon Oct 22, 2012 8:48 pm

I imagine that the speed of light delay from satellite to receiver would reduce that accuracy a little, wouldn't it? Also the relativistic time dilation of the speed of the satellites, but I think they correct that from the ground, dont they.

TheBigAndyT
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Re: Stop The Clocks

Post by TheBigAndyT » Mon Oct 22, 2012 10:52 pm

All that so we can find hidden Tupperware:)
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klossner
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Re: Stop The Clocks

Post by klossner » Fri Oct 26, 2012 6:41 pm

THE_Chris wrote:I imagine that the speed of light delay from satellite to receiver would reduce that accuracy a little, wouldn't it?
Actually, the GPSr uses that delay to determine where you are. The linked article explains it nicely.

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