[time-nuts] A first MDEV plot...

[Bert, VE2ZAZ]

Hi Everyone,


This is my first Allan Deviation plot. It consists of the PPS output of an Oncore GT+ (Navigation-grade) GPS vs. an Ovenaire 10MHz OCXO divided down to 1Hz via an HP 5328A counter. The HP 5370A is free running on its 10811-60101 OCXO. The control/plotting is done by KE5FX's T.I. utility software.

The curve clearly shows the limitations of the GPS at Tau=1s... But what else can be said of the GPS, or of the test setup when looking at the plots? 

One thing I see is that the bottom valley is much more pronounced when plotting MDEV, whereas with ADEV the curve barely breaks. How much more revealing is the MDEV curve in this case, and what effect is shown here? What dominant factor causes the valley. Is it hitting a noise floor, a true GPS performance deterioration or is is simply a calculation artefact?

I use the HP 5328A as a divider by 10 million. This is a very useful feature if you own one of these counters. I presume that a straight line plot gives a warm feeling about the divider performance, but it would be great if someone on this list who owns a HP 5328A could characterise the Timebase Output when dividing by 10 million. I will try some measurements using the 5370A and one of my OCXOs, but I am not sure I own what is necessary to make valuable measurements.

So much to learn! So much to try!

Thanks,

Bert.



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