[time-nuts] Reality check - understanding MV89A aging figures

[Matthias Welwarsky]

Hi,

since I'm using the MV89A timebase of my counter for all measurements, this 
should provide a possibility to also evaluate the stability of that timebase, 
shouldn't it?

When I measure a GPSDO, while it is locked the long term stability will be as 
good as the GPS clock. Therefore, all drift I'm seeing in the measurements 
will be from the counter timebase.

Now, TimeLab tells me the drift is around 3E-5 Hz per hour. Pulling up the 
well-known datasheet for the MV89A, depending on the OCXO class the aging is 
between +/- 3e-8 and +/- 5e-9  per year. Since no unit is given on the data 
sheet I'm assuming it is relative accuracy, right?

The datasheet doesn't give daily aging figures but states that the typical 
correspondence between yearly and daily is a factor of 1e-2.

Therefore, is the following calculation correct:

5e-9 / year => 5e-11 / day => around 2e-12 / hour, relative accuracy

2e-12 / hour * 10 MHz = 2e-5 Hz / hour

If that's correct, my timebase would be still in spec, not best in class but 
quite OK, at least as far as aging is concerned.

BR,
Matthias