[time-nuts] ublox NEO-M8T improved by insulated chamber?
Tom Van Baak
tvb at LeapSecond.com
Tue Nov 7 23:16:09 EST 2017
> Which is small compared to the published GPS time resolution (IS_GPS_200H,
> page 54) of 90 ns.
Correct. GPS performs far better than the original spec. Like the Mars rovers...
As a result we're now all used to ~10 ns level of performance out of GPS, even in a $5 receiver. Closer to ~1 ns is possible when you dig into the bag-of-timing-tricks like zero-D mode, sawtooth correction, antenna calibration, multi-path mitigating antennae, dual-frequency receivers, external frequency references, post-processing, temperature stabilization of antenna, cables, receiver, etc. So the industry big boys are getting sub-cm levels of positioning and sub-ns levels of timing. It's all pretty cool. Some time nuts are not far behind.
Note also that relative timing, such as needed by a GPSDO frequency standard is always much better than absolute timing, such as needed by a UTC time standard. This is because many of the unknown offsets (antenna, cable, receiver RF and f/w) magically cancel when used as a GPSDO. This is why some GPSDO can get down to parts in 10^14th frequency stability over a day.
There's a slide I remember seeing that shows how GPS timing accuracy has improved since the early days. It's page 9 (attached) of:
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