On 8/29/2011 11:57 PM, NPG wrote:
On 8/29/2011 9:47 PM, unruh wrote:
On 2011-08-29, NPG<nat...@cmpublishers.com> wrote:
On 8/29/2011 5:03 PM, Chris Albertson wrote:
On Mon, Aug 29, 2011 at 12:43 PM, NPG<nat...@cmpublishers.com> wrote:
Stupid noob question alert.
Does GPS provide better accuracy?
Depending on which GPS receiver, GPS can be MANY orders of magnitude better.
The best GPSes have a one sigma error on the pulse per second that is on
the order of 5 nanoseconds or less. At this level we need carfully measure
cable lengths and allow for the speed of light delay and "velocity factor"
of the cable. We are talking about literally 10,000 or even a million
times better, literally.
LOL, I only vaguely understand what you are talking about.
That said if the GPS is only being used to drive NTP we don't need
nanosecond level accuracy.
OK, I guess I don't necessarily need to understand the above.
Not sure what you do not understand, but if nanosecond (1 billionth of a
second) confuses you then it is not clear what it is you want to do.
The time stuff I understand, even the radio wave propagation stuff,
though obviously not as well as others here.
I'm not sure what "cable length", "speed of light delay", or "velocity
factor" is all about.
My guess is its about where physics start to limit the theoretical
performance of timekeeping electronics.
The speed of light and/or electrical signals, radio waves, etc. are
*approximately* the same! The speed of an electrical signal in copper
wire is slightly less than the speed of light in vacuum! It will be
different again if the wires are aluminum rather than copper. If you
are counting nanoseconds the difference may be significant. A few
people, e.g. radio astronomers, really care about the difference. MOST
of the rest of us are less demanding!
"Get me to the church on time!"
Your doctor WILL be late for your appointment! It's a law of nature!
<snip>
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