[time-nuts] M12+T First Light

Tom Van Baak tvb at leapsecond.com
Tue Apr 19 01:17:17 EDT 2005

Hi Brooke,

Yes, the M12 timing receiver is very nice.

Attached is a preliminary plot comparing 1 PPS jitter
among four common GPS time recievers including a
M12+ with sawtooth correction.

In the plot the VP is dark blue and the M12+ is pink.
In the table below, times are RMS over 10k seconds.

31.5 ns -- Oncore VP
 9.3 ns -- CNS-1 (M12+)
 3.0 ns -- CNS-2/O1 (M12+ h/w sawtooth correction)
 1.3 ns -- standard HP 58503B (8ch VP, 10811 GPSDO)

The M12+ with sawtooth correction is yellow and
the GPSDO is green. You can see that although
the M12+ with sawtooth correction has slightly
more jitter than the GPSDO, as a time standard
on average it looks like it might be more accurate
more of the time.

As you know from playing with a 58503A or Z3801A
a GPSDO does a fair amount of wandering and you
can see this in the plot.

If you require a real-time 10 MHz or 1 PPS then use
a GPSDO but if you're collecting data only for later
processing then it looks like an M12+ with sawtooth
correction is just as good or better.


----- Original Message -----
From: "Brooke Clarke" <brooke at pacific.net>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Friday, April 15, 2005 16:23
Subject: [time-nuts] M12+T First Light

> Hi:
> To use an astronomical term "First Light" meaning my first use of the
M12+T GPS Timing receiver.  WOW!!!!
> The manual description of the @@Hn command shows -128 to +127 ns as the
range for the sawtooth error.  On the 8 channel unit I think the actual
sawtooth error was around + and - 50 ns.
> I looked at the @@Hn data stream in TAC32 and saw numbers in the mid
teens, much lower than the 8 chan sawtooth error.  I'm not sure if this is
typical, or maybe I was just lucky.  I have the El mask set to 50 degrees
and Time RAIM turned off.
> I've made a small number of measurements against the Cesium source whose C
field I haven't touched for a month or two and the standard deviation for
5,000 1 PPS measurements ranges from 14 to 27 ns, whereas the 8 channel unit
was typically in the mid 30 ns range with excursions much higher.
> So the way timing is being handled in the M12+T is far better than the old
8 channel units, i.e. it's not just more channels.
> Having Fun,
> Brooke Clarke, N6GCE

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