Super Accurate clock for your PC

Doesn't the GPS take the time from the satellites? As far as I know GPS time is accurate to within one millionth of a second, better than any NTP server!

Yeah your right, should have thought of that! I was thinking position info.

Doesn't the GPS take the time from the satellites? As far as I know GPS time is accurate to within one millionth of a second, better than any NTP server!

Yes at lightspeed then averaged over typically 3 satellites

Its as accurate as you are going to get without getting the USNO to calibrate your atomic clock for you! And the GPS satellites are set from the USNO anyway.

BTW, if you ever find yourself around the Washington D.C visiting the Observatory is very worthwhile. The 12" scope is impressive enough, but the facilities they have for for time keeping are facinating also. (If you are into racks of machines and chatting about networks...)

Cheers,
~Al

(If you are into racks of machines and chatting about networks...)

He he, I used to work for Lucent on their ATM WAN stuff, They had some pretty accurate network clocks, but alas, I think it may have turned me off racks and networks for life!

Doesn't the GPS take the time from the satellites? As far as I know GPS time is accurate to within one millionth of a second, better than any NTP server!

Its as accurate as you are going to get without getting the USNO to calibrate your atomic clock for you!

In theory! Unfortunately, the software in most GPS receivers was designed by people who weren't all that concerned with providing super-accurate time to customers, which means that you need to be careful in your interpretation of what the receiver says.

I have two Garmin GPS receivers, and, when they have acquired a lock, they are generally about 0.2 to 0.8 seconds slow (as measured against a MSF Rugby clock that I have that I trust). I believe some Magellan GPS receivers are better designed from the point of view of telling the time.

If you are willing to spend the money (maybe a few hundred) you can get GPS receivers that are accurate to a few dozen nanoseconds (ie thousandths of a millionth of a second).

When I was in UCG (many moons ago), I was involved in a project that involved pulsars. I used a super-accurate GPS receiver - this thing was making an LED flash within a couple of dozen nanoseconds of the start of each second. Unforutnately, I had difficult figuring out WHICH second it was flashing at.

So, I hooked the GPS up to one trace on an oscilloscope, and I tuned in RWM (a time signal broadcast from Moscow) into the other. I found an 11 millisecond delay between the two. Why? Because Moscow is about 3,300km from Galway, and radio waves travel at 300,000km per second!

Anyway, as a double-check, I also consulted the speaking clock. The speaking clock was giving me a different answer to what RWM was giving me - the speaking clock was saying that my GPS (and RWM) were a second slow. I contact Telecom Eireann about it. I eventually got in touch with the office that maintains the clock. It turns out that they use the DCF-77 signal (a time signal broadcast from Germany). When I asked them about the one second discrepancy, the response I got was "so what?". When I explained that I needed to know the time to within millionths of a second, I was asked "oh - do you want me to reset the clock?".

One of my colleagues said "you should have said yes - I'm late with my project"

LOL- that's quite a good story! And if you want to give one of those Magellan receivers away I know someone who may be interested :roll:
Typical Telecom Eireann....

I found another Time server, In Ireland this time- run by the chaps in Trinity

salmon.maths.tcd.ie

Unfortunately i couldn't find out anything more aboutt he clock or how precise it is, so I'll be sticking with the NIST clock for now.

Maybe some ex-Trinity student could help us out here.....)))

Unfortunately i couldn't find out anything more aboutt he clock or how precise it is, so I'll be sticking with the NIST clock for now.

Maybe some ex-Trinity student could help us out here.....)))

I went to a superior Dublin university...

This may be out of date but, as I recall:
ntp.maths.tcd.ie (aka lanczos.maths.tcd.ie) has(had?) a GPS unit, (an expensive one Colm!) and a radio reciever.

salmon and ntp.cs.tcd.ie are peered together with this so picking any will do.