[time-nuts] Common sky pps errors for any GPSDOs?

[Matt Ettus]

On Mon, Jan 5, 2009 at 9:27 PM,  <SAIDJACK at aol.com> wrote:
> Hi Matt,
>
> having 140ps matching of the 1PPS between units is the equivalent of  knowing
> your antenna position to within ~0.14 feet total error max.
>
> Thats less than one inch error per antenna!

That makes it sound a lot more difficult than it really is.  The vast
majority of the error in GPS is systematic, such that two GPS systems
with antennas near each other should have highly correlated error.
This is the basis of differential GPS.  It doesn't matter if the
absolute error is hundreds of feet, as long as  both devices have the
same error.

I spent a couple of years nearly a decade ago doing differential GPS
for steering heavy equipment.  You can get sub-centimeter errors over
baselines in the tens of km.  Again, this is relative error.

Matt