[time-nuts] ADEV vs MDEV

WarrenS warrensjmail-one at yahoo.com
Sat Feb 6 19:19:04 UTC 2010

Peat said:
>I would appreciate any comments or observations on the topic of apparatus with demonstrated stability measurements. 
>My motivation is to discover the SIMPLEST scheme for making stability measurements at the 1E-13 in 1s  performance level.

If you accept that the measurement is going to limited by the Reference Osc, 
for Low COST and SIMPLE, with the ability to measure ADEVs at that level, 
Can't beat a simple analog version of  NIST's "Tight Phase-Lock Loop Method of measuring Freq stability".  
http://tf.nist.gov/phase/Properties/one.htm#oneone    Fig 1.7

By replacing the "Voltage to freq converter, Freq counter & Printer with a Radio shack type PC data logging DVM, 
It can be up and running from scratch in under an Hr, with no high end test equipment needed.
If you want performance that exceeds the best of most DMTD at low Tau it takes a little more work 
and a higher speed oversampling ADC data logger and a good offset voltage.

I must add this is not a popular solution (Or a general Purpose one) but 
IF  you know analog and have a GOOD osc with EFC to use for the reference, 
as far as I've been able to determine it is the BEST SIMPLE answer that allows High performance.
Limited by My HP10811 Ref OSC, I'm getting better than 1e-12 in 0.1 sec (at 30 Hz Bandwidth)

Basic modified NIST Block Diag attached:
The NIST paper sums it up quite nicely:
'It is not difficult to achieve a sensitivity of a part in e14 per Hz resolution 
so one has excellent precision capabilities with this system.'

This does not address your other question of ADEV vs MDEV,  
What I've described is just a simple way to get the Low cost, GOOD Raw data.
What you then do with that Data is a different subject.

You can run the raw data thru one of the many ADEV programs out there, 'Plotter' being my choice.

Have fun 


[time-nuts] ADEV vs MDEV
Pete Rawson peterawson at earthlink.net 
Sat Feb 6 03:59:18 UTC 2010 

Efforts are underway to develop a low cost DMTD apparatus with
demonstrated stability measurements of 1E-13 in 1s. It seems that
existing TI counters can reach this goal in 10s. (using MDEV estimate
or 100+s. using ADEV estimate). The question is; does the MDEV tool
provide an appropriate measure of stability in this time range, or is
the ADEV estimate a more correct answer? 

The TI performance I'm referring to is the 20-25 ps, single shot TI,
typical for theHP5370A/B, the SR620 or the CNT81/91. I have data
from my CNT81showing MDEV < 1E-13 in 10s. and I believe the
other counters behave similarly.

I would appreciate any comments or observations on this topic.
My motivation is to discover the simplest scheme for making 
stability measurements at this performance level; this is NOT
even close to the state-of-the-art, but can still be useful.

Pete Rawson

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