[time-nuts] HP5065A environmental sensitivities

DG2OM at gmx.de DG2OM at gmx.de
Wed May 18 06:57:42 UTC 2016


This is my first contribution to the Time-Nut list, but I am a follower for several years.
I have made 30 days phase difference measurements of an HP5065a versus a modified Thunderbolt GPSDO (got a MV180 oscillator) with a Fluke PM6681,
and recorded the results with Timelap. Starting signal of the PM6681 was the 5MHz of the HP5065A, stop signal the 10MHz from the Thunderbolt. A single
measurement was triggered once a second from the PPS of the TB.
I also have a weather station at 6 km distance away, which records barometric pressure at time intervals of 10 minutes. Out from these measurements, I divided
my phase measurements into 10 minute intervals, calculated the 10 min average frequencies and made a linear regression with the 10 minute pressure measurements.
I got a slope of 3.86E-14/hPa frequency difference versus pressure.
Then I corrected the original 10 min average frequency measurements with the result from the linear regression and imported the original and the corrected
datasets into Timelap.
The influence of the barometric pressure to the ADEV for long time intervals is shown in the picture.
Just for fun, to render the pressure sensitivity visible for the human eye, I removed the noise of the GPSDO by generating a plot of overlapping 1 day
frequency averages in 10 minute time intervals. On the second picture you can compare it with the 10minute pressure data from the weather station. I think, 
it is quite impressive. The calculated slope out of these overlapping averages was with 3.74e-14/hPa a little bit different compared with the non overlapping dataset.
 
Best regards
Wulf
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