[time-nuts] Z-12T (timing) receiver

Doug Hogarth doug at niceties.com
Wed Aug 2 20:18:16 UTC 2006


> I think the method is still in development and Doug Hogarth is helping.  

As someone else mentioned, the Z-12 receivers are discontinued and no longer
supported by Thales.  They do work well and are used widely, and I believe
an individual in England still considers repairing them.  Cost was in the
$20K range and it cost something like $5K extra for the timing-specific
option.

Compared to typical dual-frequency carrier-phase receivers, a few key
differences of the Z-12T are: 1) the receiver has a 1PPS *input* which is
used to sync the receiver's timing to a reproducible zero-crossing of the
reference frequency, 2) in the case of the Z-12T the input frequency of
20MHz is more directly used by the receiver, 3) the precise timing community
conducts experiments with the receiver such as absolute and/or relative
calibration (and comparison to other methods such as common-view and/or
TWSTT).  Note that Javad has similar carrier-phase timing capability but
might not have as many experiments/calibrations.

People like me don't use the 1PPS out from receiver, rather we supply our
best clock's frequency to the receiver and log RINEX data with carrier
phase.  The data from similar receivers around the world including H-masers
at various national timing labs is combined and processed regularly by IGS
analysis centers.  They produce precise orbits and satellite clocks and
"ensemble" time, and the final result is that you can get a difference
between your clock and one of the other clocks, typically a point every five
minutes available a couple weeks after real-time.

Saying "experiment" is mostly because common-view has been so widely
accepted over the years, and expensive TWSTT (Two-Way Satellite Time
Tranfer) is more widely accepted for higher precision.  Not so many people
trust the carrier-phase method but it works well for me; similarly I'm part
of JPL's "real-time" system which gives me difference between my clock and
AMC every second with just a few seconds delay.

So to be clear, this is not typical inexpensive code-based single-frequency
"one-way" GPS timing; the carrier-phase data is often used in other products
such as precise orbits/clocks (which are used by geodetic community).






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