[time-nuts] Comparing the performance of 17 different GPSDOs

[Magnus Danielson]

Hi Mark,

First of all, congratulation on good work, as always.

I think the way of presenting it makes it somewhat hard to get an
overview. I think you should do a proper paper on it. This would have
been interesting to have as a paper for IFCS/EFTF. Cut-off date passed.

It would be nice with a table listing performance for a couple of key taus.

The one thing that I wonder is how much localization error of the
receivers can be judged to have effected their performance. If they
where not fed the same position, some deviation may be to how well they
averaged in a fixed location, which may vary from time to time and that
other processes od the receiver where overshadowed by how well they
where located.

Cheers,
Magnus

On 12/9/18 6:10 AM, Mark Sims wrote:
> I recently completed some comparison tests of the PPS and 10 MHz outputs of 17 different GPSDOs.
> 
> The tests were done with a TAPR TICC time interval counter running in timestamp mode and the data was acquired and processed with Lady Heather.   The TICC was clocked by a HP-5071A cesium beam oscillator with the high-performance tube.   The TICC has a resolution of around 60 picoseconds.
> 
> The PPS signal from the GPSDO was connected to channel A of the TICC (for those GPSDOs that have an easily accessible PPS signal).  For receivers without a PPS signal available, Heather shows ADEV, HDEV, MDEV, and TDEV data for the 10 MHz signal.   For receivers with a PPS,  ADEV is shown for the 1PPS and 10 MHz signals.
> 
> The GPSDO output frequency (10 MHZ) was connected to channel B of the TICC through a TAPR TADD-2 Mini divider to get a 1 Hz output.
> 
> Note that PPS and 10 MHz plots have a display averaging filter applied.   Without this filter the plots mostly show noisy "grass" and not any interesting details.  A side effect of the display filter is to reduce the "span" (difference between the max and min values seen) of the plot data.  Typically the unfiltered spans are around twice the value shown in the plot header, but for a couple of receivers it is up to a 10x reduction of the raw span.
> 
> Each GPSDO was allowed to warm up for at least 24 hours,  or longer... until the DAC output voltage slope leveled off.
> 
> The GPSDO antenna was a L1/L2/GPS/GLONASS/BEIDOU antenna from China.  With a L1/L2 survey receiver this antenna produces location error ellipse in the 5-10mm range.  It is mounted on a 1 meter tripod and fed into an 8-way amplified L1/L2/Glonass/Beidou splitter.  The antenna is in a rather horrible location for multi-path and sky view.   Lots of tall trees and a 2 story stucco-over-wire mesh house.
> 
> http://www.eevblog.com/forum/metrology/comparing-the-performance-of-17-different-gpsdos/msg2025295/#msg2025295
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