Peat said:

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
ws

[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

Hi

It's possible / likely to injection lock with the tight loop approach and get data that's much better than reality. A lot depends on the specific oscillators under test and the buffers (if any) between the oscillators and mixer.

If your OCVCXO has a tuning slope of 0.1 ppm / volt then a part in 10^14 is going to be at the 100 of nanovolts level. Certainly not impossible, but it does present it's own set of issues. Lab gear to do it is available, but not all that common. DC offsets and their temperature coefficients along with thermocouple effects could make things exciting.

There is no perfect way to do any of this, only a lot of compromises here or there. Each approach has stuff you need to watch out for.

Bob

From: "WarrenS" warrensjmail-one@yahoo.com
Sent: Saturday, February 06, 2010 2:19 PM
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Subject: Re: [time-nuts] ADEV vs MDEV

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Peat said:

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
ws

[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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To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Sounds good but you still haven't found its Achilles heel:

The frequency measures need to be integrated (either implicitly or
explicitly) to produce phase measures which can then be used to
calculate ADEV, MDEV etc.
The major problem is that integration amplifies the small errors that
are inevitably present.
In practice (except for very noisy sources) the technique isnt
particularly useful for Tau more than a few times the inverse PLL
bandwidth.

Thus NIST and others quietly dropped this method several decades ago.
This is alluded to in Steins recent paper availble on the Symmetricom
website:

The Allan Variance – Challenges and Opportunities

Bruce

WarrenS wrote:

Peat said:

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
ws

[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

Hi

It's possible / likely to injection lock with the tight loop approach and get data that's much better than reality. A lot depends on the specific oscillators under test and the buffers (if any) between the oscillators and mixer.

If your OCVCXO has a tuning slope of 0.1 ppm / volt then a part in 10^14 is going to be at the 100 of nanovolts level. Certainly not impossible, but it does present it's own set of issues. Lab gear to do it is available, but not all that common. DC offsets and their temperature coefficients along with thermocouple effects could make things exciting.

There is no perfect way to do any of this, only a lot of compromises here or there. Each approach has stuff you need to watch out for.

Bob

From: "WarrenS" warrensjmail-one@yahoo.com
Sent: Saturday, February 06, 2010 2:19 PM
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Subject: Re: [time-nuts] ADEV vs MDEV

Something I certainly worried about and tested for.
What I found (for MY case) is that injection lock is NOT a problem.
The reason being is that unlike most other ways, where the two OSC have to be completely independent,
The tight loop approach forces the Two Osc to "Lock with something like 60 + db gain,
so a little stray -80db injection lock coupling that would very much limit other systems has
no measurable effect at e-13. Just one of the neat little side effects that make the tight loop approach so simple.

For that example, just need to put a simple discrete 100 to 1 resistor divider
in-between the control voltage and the EFC and now you have a nice workable 10uv.
BUT the bigger point is, probable not needed, cause you are NOT going to do any better than the stability of the OSC with a grounded shorted EFC input.

as you said and I agree is so true:

But you did not offer any easier way to do it, which is what the original request was for and my answer addressed.
This is the cheapest easiest way BY FAR to get high performance, at low tau, ADEV numbers that I've seen.

ws

----- Original Message ----- From: "Bob Camp"lists@cq.nu
To: "Discussion of precise time and frequency measurement"time-nuts@febo.com
Sent: Saturday, February 06, 2010 12:09 PM
Subject: Re: [time-nuts] ADEV vs MDEV

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