[time-nuts] Is it Hz or MHz ?

wb6bnq wb6bnq at cox.net
Mon Jun 2 04:17:41 EDT 2014

Hi Kit,

The value of 5E^-11 refers to the resolution that the precision can be 
relied upon after taking into account all the factors that influence 
it.  It means that there is an error that can be as much as +/-5 parts 
per e^-11.

At 10 MHz that is +/- 0.0005 Hertz error.  At 5 MHz that is +/-0.00025 
Hertz error.  At 1 MHz it is +/-0.00005 Hertz error.  And, finally, at 1 
Hertz it is +/-0.00000000005 Hertz error.


Kit Scally wrote:

>Team Nutters,
>GPSDO's are often specified for stability as so many parts per x.  Using a
>Symmetricom 8040C as an example, this has a quoted accuracy of typically
>5E^-11 at shipment.  Ageing (monthly and yearly) and ADEV stability rates
>for 1, 10 & 100 seconds are also given. This particular device as 1, 5 and
>10 MHz outputs.
>The question - is this "accuracy" with respect to 1Hz - or 10MHz ?  If the
>latter, then the accuracy figures quoted needs to be modified by 10^6 (Hz to
>MHz) to get a feel for the actual frequency changes at 10MHz.
>Glossies of many GPSDO manufacturers seem deathly silent on this point, so
>clearly, "something is assumed".  I have seen an oscillator comparison chart
>by Meinberg (a German company) that in their comparison chart, the accuracy
>references need scaling to relate to 1Hz.
>Appreciate some advice and/or direction on this before madness overtakes me
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