[time-nuts] Testing frequency using NTP Bruce GPS ps

Tom Van Baak tvb at LeapSecond.com
Mon Oct 13 15:29:51 UTC 2008


Mike,

>  So where did the 1ns granularity come in?

For example, Motorola receivers output the sawtooth correction as
an 8-bit signed binary field in the @@En/Hn TRAIM message. The
range of said byte is -128 to +127; the scale, the granularity, the
units of that field are 1 ns. Make sense now?

>  Thanks, already studied and analyzed. He uses an XOR phase detector,
>  but the  funny hump at 1,000 seconds bothers me. I can't see  a good
>  reason for  that.  The drop starting at 1e4 is  interesting,  and it
>  would have been nice to see what happens further out.

The hump around 1000 seconds is characteristic of quartz-based
GPSDO. It is related to the "cross-over point" where the instability
of the XO meets the stability of GPS on an ADEV plot and to the
time-constant of the PLL.

Here's another GPSDO related link for you to study.
http://www.thinksrs.com/assets/instr/PRS10/PRS10diag2.htm
http://www.thinksrs.com/products/PRS10.htm

/tvb





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