[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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