[time-nuts] Trying a slow sweep to assess the accuracy of a frequency counter

[Erik Kaashoek]

To get more insight in the performance of a frequency counter when 
measuring difficult frequencies, a slow (500 s) sweep with center of 10 
MHz and a span of +/- 5 Hz was generated
The frequency counter is set to 1 s gate time. Both the counter and the 
signal generator where locked to the same external reference.
Attached picture shows the linear residue of the frequency difference. 
CVS file with the raw frequency measurements also attached.
The slow oscillations outside +/1 Hz deviation could be caused by the 
limited sample speed and DAC resolution of the used signal generator.
Between +/- 1 Hz deviation the measurement noise increases as the 
contribution of the linear regression in the counter seems to decrease.
The ADEV calculated after removing the sweep trend is about 2e-11 for 
tau from 1 to 10 s
Outside the +/- 1 Hz deviation the ADEV seems to be well below 1e-11 
with tau is 1 s
Does this measurement make sense?
Any suggestions on how to improve this stress test?
Erik.
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