[time-nuts] ublox NEO-M8T improved by insulated chamber?

[Tom Van Baak]

Gary,

> 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:

https://www.gps.gov/cgsic/meetings/2013/matsakis.pdf

/tvb
-------------- next part --------------
A non-text attachment was scrubbed...
Name: cgsic-2013-matsakis-p9.png
Type: image/png
Size: 190382 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20171107/88fed88c/attachment.png>