W
WarrenS
Sat, Feb 6, 2010 10:15 PM
Yes I agree there are all kinds of ways to do it wrong, and some ways to do
it better,
The original NIST uses a VtoF converter and then a counter to do the Freq
integration 'directly' (NO Phase info needed).
This can all be replaced with a simple RC and a oversampling ADC and a
little knowledge.
A simple DVM that updates and records at say two to 4 per second AND has an
internal under 1 second filter TC,
does the "average Freq over time" good enough NOT to be a problem, when that
data is then used for 1 sec and slower Tau.
OK. SO need to use an RC pre-averager, and need to be careful with the
sample rate and not 'push' it too far to get the "Direct integration",
But with just a little thought, you have NO aliasing and you get perfect
enough integration with no dead time using a oversampling.
(I use 1 KHz over-sampling to do near perfect 10 Hz integration and OK 100Hz
integrated data.)
Easy yes, BUT, You failed to mention that to get the same sub 0.1ps TI phase
resolution and performance that the simple "Tight Phase-Lock Loop Method"
gives for free, will take a lot more than "easy".
So if one of your points is that one has to be careful and know what they
are doing, ... We Agree.
or that there are ways to do better given an unlimited budget ...We Agree
Or this is not the simplest and cheapest way to get 1e13 resolution at 1
sec... You have NOT yet commented on that so I don't know if we agree?
Just so things do not get too far off the original topic that happens all to
often, here is a reminder:
"I would appreciate any comments or observations on the SIMPLEST scheme
for making stability measurements at 1e-13 in one sec."
ws Answer) Try the "Tight Phase-Lock Loop Method"
ws
----- Original Message -----
From: "Bruce Griffiths" bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, February 06, 2010 1:16 PM
Subject: Re: [time-nuts] ADEV vs MDEV
The tight PLL method doesn't directly produce the average frequency over
Tau.
As explained in (see snapshot of relevant section):
NIST special Publication 1065 Handbook of Frequency Stability Analysis
http://tf.nist.gov/timefreq/general/pdf/2220.pdf
the average frequency deviations for averaging time Tau are needed for
the calculation.
You need to sample at a sufficiently high rate to avoid aliasing and
average (ie integrate) the individual EFC samples.
If one uses phase measures then the fluctuations in the frequency
averages can easily and directly calculated from the difference between
the phase measured at time intervals separated by Tau.
Bruce
WarrenS wrote:
Thus NIST and others quietly dropped this method several decades ago.
Could it be another reason?
I'll bet that was after they wanted to do better than 1e14 resolution
AND had unlimited amounts of time and Money,
Something most time Nuts are not blessed with. I Never said it was
the BEST way.
JUST given the goal, which was 1e13 in one second, there is not a
simpler and cheaper way to do it.
And nothing you said counter that point.
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.
Well ONE of us certainly has something backward.
To calculate ADEV, MDEV etc. YOU need Freq Differences.
The first thing that happens when phase is used is that it is turned
into Freq by taking the difference between each sample.
Integrated Freq data, which is what "Tight Phase-Lock Loop Method"
gives you directly (no Phase conversion needed),
Need not FIRST turned into Phase so that it can then be turned back
into Freq.
BUT in any case there is no difference in the noise, for a given
bandwidth, If you don't run out of digits and You have enough resolution.
The "Tight Phase-Lock Loop Method" can EASY get sub pS resolution,
which is better than most other ways.
AND don't need filters and slue rate control and multistage limiters
and on & on to do it, an RC works fine to replace all the stuff.
ws
----- Original Message ----- From: "Bruce Griffiths"
bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, February 06, 2010 12:11 PM
Subject: Re: [time-nuts] ADEV vs MDEV
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:
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
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
Yes I agree there are all kinds of ways to do it wrong, and some ways to do
it better,
The original NIST uses a VtoF converter and then a counter to do the Freq
integration 'directly' (NO Phase info needed).
This can all be replaced with a simple RC and a oversampling ADC and a
little knowledge.
A simple DVM that updates and records at say two to 4 per second AND has an
internal under 1 second filter TC,
does the "average Freq over time" good enough NOT to be a problem, when that
data is then used for 1 sec and slower Tau.
OK. SO need to use an RC pre-averager, and need to be careful with the
sample rate and not 'push' it too far to get the "Direct integration",
But with just a little thought, you have NO aliasing and you get perfect
enough integration with no dead time using a oversampling.
(I use 1 KHz over-sampling to do near perfect 10 Hz integration and OK 100Hz
integrated data.)
> If one uses phase ...
Easy yes, BUT, You failed to mention that to get the same sub 0.1ps TI phase
resolution and performance that the simple "Tight Phase-Lock Loop Method"
gives for free, will take a lot more than "easy".
So if one of your points is that one has to be careful and know what they
are doing, ... We Agree.
or that there are ways to do better given an unlimited budget ...We Agree
Or this is not the simplest and cheapest way to get 1e13 resolution at 1
sec... You have NOT yet commented on that so I don't know if we agree?
Just so things do not get too far off the original topic that happens all to
often, here is a reminder:
>>>> "I would appreciate any comments or observations on the SIMPLEST scheme
>>>> for making stability measurements at 1e-13 in one sec."
ws Answer) Try the "Tight Phase-Lock Loop Method"
ws
**************
----- Original Message -----
From: "Bruce Griffiths" <bruce.griffiths@xtra.co.nz>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Saturday, February 06, 2010 1:16 PM
Subject: Re: [time-nuts] ADEV vs MDEV
> The tight PLL method doesn't directly produce the average frequency over
> Tau.
> As explained in (see snapshot of relevant section):
> NIST special Publication 1065 Handbook of Frequency Stability Analysis
> <http://tf.nist.gov/timefreq/general/pdf/2220.pdf>
> the average frequency deviations for averaging time Tau are needed for
> the calculation.
> You need to sample at a sufficiently high rate to avoid aliasing and
> average (ie integrate) the individual EFC samples.
>
> If one uses phase measures then the fluctuations in the frequency
> averages can easily and directly calculated from the difference between
> the phase measured at time intervals separated by Tau.
>
> Bruce
>
> WarrenS wrote:
>> Bruce said:
>>
>>> Thus NIST and others quietly dropped this method several decades ago.
>> Could it be another reason?
>> I'll bet that was after they wanted to do better than 1e14 resolution
>> AND had unlimited amounts of time and Money,
>> Something most time Nuts are not blessed with. I Never said it was
>> the BEST way.
>> JUST given the goal, which was 1e13 in one second, there is not a
>> simpler and cheaper way to do it.
>> And nothing you said counter that point.
>>
>>
>>> 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.
>>
>> Well ONE of us certainly has something backward.
>> To calculate ADEV, MDEV etc. YOU need Freq Differences.
>> The first thing that happens when phase is used is that it is turned
>> into Freq by taking the difference between each sample.
>> Integrated Freq data, which is what "Tight Phase-Lock Loop Method"
>> gives you directly (no Phase conversion needed),
>> Need not FIRST turned into Phase so that it can then be turned back
>> into Freq.
>> BUT in any case there is no difference in the noise, for a given
>> bandwidth, If you don't run out of digits and You have enough resolution.
>> The "Tight Phase-Lock Loop Method" can EASY get sub pS resolution,
>> which is better than most other ways.
>> AND don't need filters and slue rate control and multistage limiters
>> and on & on to do it, an RC works fine to replace all the stuff.
>>
>> ws
>>
>> *****************
>>
>> ----- Original Message ----- From: "Bruce Griffiths"
>> <bruce.griffiths@xtra.co.nz>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts@febo.com>
>> Sent: Saturday, February 06, 2010 12:11 PM
>> Subject: Re: [time-nuts] ADEV vs MDEV
>>
>>
>>> 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:
>>>>
>>>>> 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
>>>> 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
>>>>
>
BG
Bruce Griffiths
Sat, Feb 6, 2010 10:24 PM
Another way of looking at the problem is:
One has to reconstruct the phase evolution with time by integrating the
instantaneous frequency.
Then if the resultant phase evolution is sampled every Tau seconds and
the first differences taken and divided by Tau the result is a sequence
of average frequency samples required by the AVAR formula.
However its easier just to use the sampled phases in the alternative
formula.
With the tight PLL method one has a sequence of frequency samples
averaged over an interval on the order of the inverse PLL loop bandwidth.
One then has to use these samples to reconstruct the phase evolution
over time.
One cannot use EFC samples spaced at intervals of Tau directly in the
ADEV formula which requires a sequence of frequency averages over an
interval of Tau.
If one ignores this requirement the resultant stability measure is not ADEV.
Bruce
Bruce Griffiths wrote:
The tight PLL method doesn't directly produce the average frequency
over Tau.
As explained in (see snapshot of relevant section):
NIST special Publication 1065 Handbook of Frequency Stability Analysis
http://tf.nist.gov/timefreq/general/pdf/2220.pdf
the average frequency deviations for averaging time Tau are needed
for the calculation.
You need to sample at a sufficiently high rate to avoid aliasing and
average (ie integrate) the individual EFC samples.
If one uses phase measures then the fluctuations in the frequency
averages can easily and directly calculated from the difference
between the phase measured at time intervals separated by Tau.
Bruce
WarrenS wrote:
Thus NIST and others quietly dropped this method several decades ago.
Could it be another reason?
I'll bet that was after they wanted to do better than 1e14 resolution
AND had unlimited amounts of time and Money,
Something most time Nuts are not blessed with. I Never said it was
the BEST way.
JUST given the goal, which was 1e13 in one second, there is not a
simpler and cheaper way to do it.
And nothing you said counter that point.
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.
Well ONE of us certainly has something backward.
To calculate ADEV, MDEV etc. YOU need Freq Differences.
The first thing that happens when phase is used is that it is turned
into Freq by taking the difference between each sample.
Integrated Freq data, which is what "Tight Phase-Lock Loop Method"
gives you directly (no Phase conversion needed),
Need not FIRST turned into Phase so that it can then be turned back
into Freq.
BUT in any case there is no difference in the noise, for a given
bandwidth, If you don't run out of digits and You have enough
resolution.
The "Tight Phase-Lock Loop Method" can EASY get sub pS resolution,
which is better than most other ways.
AND don't need filters and slue rate control and multistage limiters
and on & on to do it, an RC works fine to replace all the stuff.
ws
----- Original Message ----- From: "Bruce Griffiths"
bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, February 06, 2010 12:11 PM
Subject: Re: [time-nuts] ADEV vs MDEV
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:
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
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
Another way of looking at the problem is:
One has to reconstruct the phase evolution with time by integrating the
instantaneous frequency.
Then if the resultant phase evolution is sampled every Tau seconds and
the first differences taken and divided by Tau the result is a sequence
of average frequency samples required by the AVAR formula.
However its easier just to use the sampled phases in the alternative
formula.
With the tight PLL method one has a sequence of frequency samples
averaged over an interval on the order of the inverse PLL loop bandwidth.
One then has to use these samples to reconstruct the phase evolution
over time.
One cannot use EFC samples spaced at intervals of Tau directly in the
ADEV formula which requires a sequence of frequency averages over an
interval of Tau.
If one ignores this requirement the resultant stability measure is not ADEV.
Bruce
Bruce Griffiths wrote:
> The tight PLL method doesn't directly produce the average frequency
> over Tau.
> As explained in (see snapshot of relevant section):
> NIST special Publication 1065 Handbook of Frequency Stability Analysis
> <http://tf.nist.gov/timefreq/general/pdf/2220.pdf>
> the average frequency deviations for averaging time Tau are needed
> for the calculation.
> You need to sample at a sufficiently high rate to avoid aliasing and
> average (ie integrate) the individual EFC samples.
>
> If one uses phase measures then the fluctuations in the frequency
> averages can easily and directly calculated from the difference
> between the phase measured at time intervals separated by Tau.
>
> Bruce
>
> WarrenS wrote:
>> Bruce said:
>>
>>> Thus NIST and others quietly dropped this method several decades ago.
>> Could it be another reason?
>> I'll bet that was after they wanted to do better than 1e14 resolution
>> AND had unlimited amounts of time and Money,
>> Something most time Nuts are not blessed with. I Never said it was
>> the BEST way.
>> JUST given the goal, which was 1e13 in one second, there is not a
>> simpler and cheaper way to do it.
>> And nothing you said counter that point.
>>
>>
>>> 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.
>>
>> Well ONE of us certainly has something backward.
>> To calculate ADEV, MDEV etc. YOU need Freq Differences.
>> The first thing that happens when phase is used is that it is turned
>> into Freq by taking the difference between each sample.
>> Integrated Freq data, which is what "Tight Phase-Lock Loop Method"
>> gives you directly (no Phase conversion needed),
>> Need not FIRST turned into Phase so that it can then be turned back
>> into Freq.
>> BUT in any case there is no difference in the noise, for a given
>> bandwidth, If you don't run out of digits and You have enough
>> resolution.
>> The "Tight Phase-Lock Loop Method" can EASY get sub pS resolution,
>> which is better than most other ways.
>> AND don't need filters and slue rate control and multistage limiters
>> and on & on to do it, an RC works fine to replace all the stuff.
>>
>> ws
>>
>> *****************
>>
>> ----- Original Message ----- From: "Bruce Griffiths"
>> <bruce.griffiths@xtra.co.nz>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts@febo.com>
>> Sent: Saturday, February 06, 2010 12:11 PM
>> Subject: Re: [time-nuts] ADEV vs MDEV
>>
>>
>>> 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:
>>>>
>>>>> 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
>>>> 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
>>>>
>>>>
>>>>
BC
Bob Camp
Sat, Feb 6, 2010 10:27 PM
Hi
With most 10811 range oscillators the impact of a simple bandpass filter is low enough to not be a major issue. That's for normal lab temperatures with the circuitry in a conventional die cast box. No guarantee if you open the window and let the fresh air blow in during the run.
That's true with a heterodyne. I can see no obvious reason it would not be true on DMTD.
Bob
On Feb 6, 2010, at 5:12 PM, Bruce Griffiths wrote:
The only major issue with DMTD systems is that they undersample the phase fluctuations and hence are subject to aliasing effects.
The low pass filter has to have a bandwidth of the same order as the beat frequency or the beat frequency signal will be significantly attenuated.
Since the phase is only sampled once per beat frequency period the phase fluctuations are undersampled.
Various attempts to use both zero crossings have not been successful.
In principle if one can overcome the increased phase shift tempco associated with a bandpass filter, using a bandpass filter can in principle ensure that the phase fluctuations are oversampled.
Bruce
Bob Camp wrote:
Hi
A straight heterodyne system will get you to the floor of most 10811's with a very simple (2 stage) limiter. As with the DMTD, the counter requirements aren't really all that severe.
Bob
On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
"It's possible / likely for injection lock ... to be a problem ..."
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.
"then a part in 10^14 is going to be at the 100 of nanovolts level."
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:
"There is no perfect way to do any of this, only a lot of compromises ... you need to watch out for".
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
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
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
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
With most 10811 range oscillators the impact of a simple bandpass filter is low enough to not be a major issue. That's for normal lab temperatures with the circuitry in a conventional die cast box. No guarantee if you open the window and let the fresh air blow in during the run.
That's true with a heterodyne. I can see no obvious reason it would not be true on DMTD.
Bob
On Feb 6, 2010, at 5:12 PM, Bruce Griffiths wrote:
> The only major issue with DMTD systems is that they undersample the phase fluctuations and hence are subject to aliasing effects.
> The low pass filter has to have a bandwidth of the same order as the beat frequency or the beat frequency signal will be significantly attenuated.
> Since the phase is only sampled once per beat frequency period the phase fluctuations are undersampled.
> Various attempts to use both zero crossings have not been successful.
>
> In principle if one can overcome the increased phase shift tempco associated with a bandpass filter, using a bandpass filter can in principle ensure that the phase fluctuations are oversampled.
>
>
> Bruce
>
> Bob Camp wrote:
>> Hi
>>
>> A straight heterodyne system will get you to the floor of most 10811's with a very simple (2 stage) limiter. As with the DMTD, the counter requirements aren't really all that severe.
>>
>> Bob
>>
>>
>> On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
>>
>>
>>>
>>>> "It's possible / likely for injection lock ... to be a problem ..."
>>>>
>>> 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.
>>>
>>>
>>>> "then a part in 10^14 is going to be at the 100 of nanovolts level."
>>>>
>>> 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:
>>>
>>>> "There is no perfect way to do any of this, only a lot of compromises ... you need to watch out for".
>>>>
>>> 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
>>>
>>>
>>>
>>>> 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
>>>>
>>>>
>>>>> 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
>>>>> 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
>>>>>
>>>>>
>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>>
>>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>>
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
BG
Bruce Griffiths
Sat, Feb 6, 2010 10:32 PM
The actual conversion algorithm used by the DVM is critical.
You actually need to use a standard integrating DVM with no deadtime
between measurements or extra filtering.
Few DVMs actually have zero deadtime between measurements.
Some of the more recent ones may have.
Have you actually modeled the effect of a small constant frequency error
or are you just hand waving?
WarrenS wrote:
Yes I agree there are all kinds of ways to do it wrong, and some ways
to do it better,
The original NIST uses a VtoF converter and then a counter to do the
Freq integration 'directly' (NO Phase info needed).
This can all be replaced with a simple RC and a oversampling ADC and a
little knowledge.
A simple DVM that updates and records at say two to 4 per second AND
has an internal under 1 second filter TC,
does the "average Freq over time" good enough NOT to be a problem,
when that data is then used for 1 sec and slower Tau.
OK. SO need to use an RC pre-averager, and need to be careful with
the sample rate and not 'push' it too far to get the "Direct
integration",
But with just a little thought, you have NO aliasing and you get
perfect enough integration with no dead time using a oversampling.
(I use 1 KHz over-sampling to do near perfect 10 Hz integration and OK
100Hz integrated data.)
Easy yes, BUT, You failed to mention that to get the same sub 0.1ps TI
phase resolution and performance that the simple "Tight Phase-Lock
Loop Method" gives for free, will take a lot more than "easy".
So if one of your points is that one has to be careful and know what
they are doing, ... We Agree.
or that there are ways to do better given an unlimited budget ...We Agree
Or this is not the simplest and cheapest way to get 1e13 resolution at
1 sec... You have NOT yet commented on that so I don't know if we agree?
Just so things do not get too far off the original topic that happens
all to often, here is a reminder:
"I would appreciate any comments or observations on the SIMPLEST
scheme for making stability measurements at 1e-13 in one sec."
ws Answer) Try the "Tight Phase-Lock Loop Method"
ws
----- Original Message ----- From: "Bruce Griffiths"
bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, February 06, 2010 1:16 PM
Subject: Re: [time-nuts] ADEV vs MDEV
The tight PLL method doesn't directly produce the average frequency over
Tau.
As explained in (see snapshot of relevant section):
NIST special Publication 1065 Handbook of Frequency Stability Analysis
http://tf.nist.gov/timefreq/general/pdf/2220.pdf
the average frequency deviations for averaging time Tau are needed for
the calculation.
You need to sample at a sufficiently high rate to avoid aliasing and
average (ie integrate) the individual EFC samples.
If one uses phase measures then the fluctuations in the frequency
averages can easily and directly calculated from the difference between
the phase measured at time intervals separated by Tau.
Bruce
WarrenS wrote:
Thus NIST and others quietly dropped this method several decades ago.
Could it be another reason?
I'll bet that was after they wanted to do better than 1e14 resolution
AND had unlimited amounts of time and Money,
Something most time Nuts are not blessed with. I Never said it was
the BEST way.
JUST given the goal, which was 1e13 in one second, there is not a
simpler and cheaper way to do it.
And nothing you said counter that point.
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.
Well ONE of us certainly has something backward.
To calculate ADEV, MDEV etc. YOU need Freq Differences.
The first thing that happens when phase is used is that it is turned
into Freq by taking the difference between each sample.
Integrated Freq data, which is what "Tight Phase-Lock Loop Method"
gives you directly (no Phase conversion needed),
Need not FIRST turned into Phase so that it can then be turned back
into Freq.
BUT in any case there is no difference in the noise, for a given
bandwidth, If you don't run out of digits and You have enough
resolution.
The "Tight Phase-Lock Loop Method" can EASY get sub pS resolution,
which is better than most other ways.
AND don't need filters and slue rate control and multistage limiters
and on & on to do it, an RC works fine to replace all the stuff.
ws
----- Original Message ----- From: "Bruce Griffiths"
bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, February 06, 2010 12:11 PM
Subject: Re: [time-nuts] ADEV vs MDEV
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:
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
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
The actual conversion algorithm used by the DVM is critical.
You actually need to use a standard integrating DVM with no deadtime
between measurements or extra filtering.
Few DVMs actually have zero deadtime between measurements.
Some of the more recent ones may have.
Have you actually modeled the effect of a small constant frequency error
or are you just hand waving?
WarrenS wrote:
>
> Yes I agree there are all kinds of ways to do it wrong, and some ways
> to do it better,
>
> The original NIST uses a VtoF converter and then a counter to do the
> Freq integration 'directly' (NO Phase info needed).
> This can all be replaced with a simple RC and a oversampling ADC and a
> little knowledge.
>
> A simple DVM that updates and records at say two to 4 per second AND
> has an internal under 1 second filter TC,
> does the "average Freq over time" good enough NOT to be a problem,
> when that data is then used for 1 sec and slower Tau.
>
> OK. SO need to use an RC pre-averager, and need to be careful with
> the sample rate and not 'push' it too far to get the "Direct
> integration",
> But with just a little thought, you have NO aliasing and you get
> perfect enough integration with no dead time using a oversampling.
> (I use 1 KHz over-sampling to do near perfect 10 Hz integration and OK
> 100Hz integrated data.)
>
>> If one uses phase ...
> Easy yes, BUT, You failed to mention that to get the same sub 0.1ps TI
> phase resolution and performance that the simple "Tight Phase-Lock
> Loop Method" gives for free, will take a lot more than "easy".
>
> So if one of your points is that one has to be careful and know what
> they are doing, ... We Agree.
> or that there are ways to do better given an unlimited budget ...We Agree
> Or this is not the simplest and cheapest way to get 1e13 resolution at
> 1 sec... You have NOT yet commented on that so I don't know if we agree?
>
> Just so things do not get too far off the original topic that happens
> all to often, here is a reminder:
>>>>> "I would appreciate any comments or observations on the SIMPLEST
>>>>> scheme for making stability measurements at 1e-13 in one sec."
> ws Answer) Try the "Tight Phase-Lock Loop Method"
>
> ws
>
> **************
>
> ----- Original Message ----- From: "Bruce Griffiths"
> <bruce.griffiths@xtra.co.nz>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts@febo.com>
> Sent: Saturday, February 06, 2010 1:16 PM
> Subject: Re: [time-nuts] ADEV vs MDEV
>
>
>> The tight PLL method doesn't directly produce the average frequency over
>> Tau.
>> As explained in (see snapshot of relevant section):
>> NIST special Publication 1065 Handbook of Frequency Stability Analysis
>> <http://tf.nist.gov/timefreq/general/pdf/2220.pdf>
>> the average frequency deviations for averaging time Tau are needed for
>> the calculation.
>> You need to sample at a sufficiently high rate to avoid aliasing and
>> average (ie integrate) the individual EFC samples.
>>
>> If one uses phase measures then the fluctuations in the frequency
>> averages can easily and directly calculated from the difference between
>> the phase measured at time intervals separated by Tau.
>>
>> Bruce
>>
>> WarrenS wrote:
>>> Bruce said:
>>>
>>>> Thus NIST and others quietly dropped this method several decades ago.
>>> Could it be another reason?
>>> I'll bet that was after they wanted to do better than 1e14 resolution
>>> AND had unlimited amounts of time and Money,
>>> Something most time Nuts are not blessed with. I Never said it was
>>> the BEST way.
>>> JUST given the goal, which was 1e13 in one second, there is not a
>>> simpler and cheaper way to do it.
>>> And nothing you said counter that point.
>>>
>>>
>>>> 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.
>>>
>>> Well ONE of us certainly has something backward.
>>> To calculate ADEV, MDEV etc. YOU need Freq Differences.
>>> The first thing that happens when phase is used is that it is turned
>>> into Freq by taking the difference between each sample.
>>> Integrated Freq data, which is what "Tight Phase-Lock Loop Method"
>>> gives you directly (no Phase conversion needed),
>>> Need not FIRST turned into Phase so that it can then be turned back
>>> into Freq.
>>> BUT in any case there is no difference in the noise, for a given
>>> bandwidth, If you don't run out of digits and You have enough
>>> resolution.
>>> The "Tight Phase-Lock Loop Method" can EASY get sub pS resolution,
>>> which is better than most other ways.
>>> AND don't need filters and slue rate control and multistage limiters
>>> and on & on to do it, an RC works fine to replace all the stuff.
>>>
>>> ws
>>>
>>> *****************
>>>
>>> ----- Original Message ----- From: "Bruce Griffiths"
>>> <bruce.griffiths@xtra.co.nz>
>>> To: "Discussion of precise time and frequency measurement"
>>> <time-nuts@febo.com>
>>> Sent: Saturday, February 06, 2010 12:11 PM
>>> Subject: Re: [time-nuts] ADEV vs MDEV
>>>
>>>
>>>> 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:
>>>>>
>>>>>> 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
>>>>> 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
>>>>>
>
>>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
W
WarrenS
Sat, Feb 6, 2010 10:42 PM
Bob
So, if your point is that there are other ways to do it. ...We Agree
(And the reason for the advanced methods is so that the counter resolution
is not the limiting factor)
Or are you saying a Tight Phase-Lock Loop" is not the simplest and cheapest
way to get 1e13 resolution at 1 sec?
That I'd have to see something new to believe it.
Just so things do not get too far off the original topic, here is a
reminder:
"I would appreciate any comments or observations on the SIMPLEST scheme
for making stability measurements at 1e-13 in one sec."
ws Answer) Try the "Tight Phase-Lock Loop Method"
May want to compare the blocks and equipment needed for A straight
heterodyne system, or a DMTD, compared to the Analog "Tight Phase-Lock Loop"
Method, AND then see what added problems there are because of injection
locking, Osc coupling, Phase noise, ETC, ETC.
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 2:03 PM
Subject: Re: [time-nuts] ADEV vs MDEV
Hi
A straight heterodyne system will get you to the floor of most 10811's with
a very simple (2 stage) limiter.
As with the DMTD, the counter requirements aren't really all that severe.
Bob
On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
"It's possible / likely for injection lock ... to be a problem ..."
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.
"then a part in 10^14 is going to be at the 100 of nanovolts level."
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:
"There is no perfect way to do any of this, only a lot of compromises ...
you need to watch out for".
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
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
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
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
Bob
So, if your point is that there are other ways to do it. ...We Agree
(And the reason for the advanced methods is so that the counter resolution
is not the limiting factor)
Or are you saying a Tight Phase-Lock Loop" is not the simplest and cheapest
way to get 1e13 resolution at 1 sec?
That I'd have to see something new to believe it.
Just so things do not get too far off the original topic, here is a
reminder:
>>>> "I would appreciate any comments or observations on the SIMPLEST scheme
>>>> for making stability measurements at 1e-13 in one sec."
ws Answer) Try the "Tight Phase-Lock Loop Method"
May want to compare the blocks and equipment needed for A straight
heterodyne system, or a DMTD, compared to the Analog "Tight Phase-Lock Loop"
Method, AND then see what added problems there are because of injection
locking, Osc coupling, Phase noise, ETC, ETC.
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 2:03 PM
Subject: Re: [time-nuts] ADEV vs MDEV
Hi
A straight heterodyne system will get you to the floor of most 10811's with
a very simple (2 stage) limiter.
As with the DMTD, the counter requirements aren't really all that severe.
Bob
*********************
On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
>
>> "It's possible / likely for injection lock ... to be a problem ..."
> 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.
>
>> "then a part in 10^14 is going to be at the 100 of nanovolts level."
> 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:
>> "There is no perfect way to do any of this, only a lot of compromises ...
>> you need to watch out for".
> 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
>
>
>> 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
>>
>>>
>>> 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
>>> 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
>>>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
BG
Bruce Griffiths
Sat, Feb 6, 2010 10:45 PM
If one were to use a bandpass filter with a Q of 10 to filter the beat
frequency output of the mixer, then if the input frequency is 10MHz and
the filter component tempco is 100ppm/C then the resultant phase shift
tempco is about 16ps/C referred to the mixer input frequency.
This phase shift tempco is certainly low enough not to have significant
impact when measuring the frequency stability of a typical 10811A if
the temperature fluctuations are kept small enough during the run.
The effect of using a bandpass filter with too narrow a bandwidth is to
artificially reduce ADEV for small Tau, so it may be prudent to use a
higher beat frequency that 1Hz or even 10Hz and not calculate ADEV for
Tau less than say 10(??) times the beat frequency period. A trade off
between this and the effect of aliasing is required.
Bruce
Bob Camp wrote:
Hi
With most 10811 range oscillators the impact of a simple bandpass filter is low enough to not be a major issue. That's for normal lab temperatures with the circuitry in a conventional die cast box. No guarantee if you open the window and let the fresh air blow in during the run.
That's true with a heterodyne. I can see no obvious reason it would not be true on DMTD.
Bob
On Feb 6, 2010, at 5:12 PM, Bruce Griffiths wrote:
The only major issue with DMTD systems is that they undersample the phase fluctuations and hence are subject to aliasing effects.
The low pass filter has to have a bandwidth of the same order as the beat frequency or the beat frequency signal will be significantly attenuated.
Since the phase is only sampled once per beat frequency period the phase fluctuations are undersampled.
Various attempts to use both zero crossings have not been successful.
In principle if one can overcome the increased phase shift tempco associated with a bandpass filter, using a bandpass filter can in principle ensure that the phase fluctuations are oversampled.
Bruce
Bob Camp wrote:
Hi
A straight heterodyne system will get you to the floor of most 10811's with a very simple (2 stage) limiter. As with the DMTD, the counter requirements aren't really all that severe.
Bob
On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
"It's possible / likely for injection lock ... to be a problem ..."
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.
"then a part in 10^14 is going to be at the 100 of nanovolts level."
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:
"There is no perfect way to do any of this, only a lot of compromises ... you need to watch out for".
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
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
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
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
If one were to use a bandpass filter with a Q of 10 to filter the beat
frequency output of the mixer, then if the input frequency is 10MHz and
the filter component tempco is 100ppm/C then the resultant phase shift
tempco is about 16ps/C referred to the mixer input frequency.
This phase shift tempco is certainly low enough not to have significant
impact when measuring the frequency stability of a typical 10811A if
the temperature fluctuations are kept small enough during the run.
The effect of using a bandpass filter with too narrow a bandwidth is to
artificially reduce ADEV for small Tau, so it may be prudent to use a
higher beat frequency that 1Hz or even 10Hz and not calculate ADEV for
Tau less than say 10(??) times the beat frequency period. A trade off
between this and the effect of aliasing is required.
Bruce
Bob Camp wrote:
> Hi
>
> With most 10811 range oscillators the impact of a simple bandpass filter is low enough to not be a major issue. That's for normal lab temperatures with the circuitry in a conventional die cast box. No guarantee if you open the window and let the fresh air blow in during the run.
>
> That's true with a heterodyne. I can see no obvious reason it would not be true on DMTD.
>
> Bob
>
>
> On Feb 6, 2010, at 5:12 PM, Bruce Griffiths wrote:
>
>
>> The only major issue with DMTD systems is that they undersample the phase fluctuations and hence are subject to aliasing effects.
>> The low pass filter has to have a bandwidth of the same order as the beat frequency or the beat frequency signal will be significantly attenuated.
>> Since the phase is only sampled once per beat frequency period the phase fluctuations are undersampled.
>> Various attempts to use both zero crossings have not been successful.
>>
>> In principle if one can overcome the increased phase shift tempco associated with a bandpass filter, using a bandpass filter can in principle ensure that the phase fluctuations are oversampled.
>>
>>
>> Bruce
>>
>> Bob Camp wrote:
>>
>>> Hi
>>>
>>> A straight heterodyne system will get you to the floor of most 10811's with a very simple (2 stage) limiter. As with the DMTD, the counter requirements aren't really all that severe.
>>>
>>> Bob
>>>
>>>
>>> On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
>>>
>>>
>>>
>>>>
>>>>
>>>>> "It's possible / likely for injection lock ... to be a problem ..."
>>>>>
>>>>>
>>>> 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.
>>>>
>>>>
>>>>
>>>>> "then a part in 10^14 is going to be at the 100 of nanovolts level."
>>>>>
>>>>>
>>>> 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:
>>>>
>>>>
>>>>> "There is no perfect way to do any of this, only a lot of compromises ... you need to watch out for".
>>>>>
>>>>>
>>>> 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
>>>>
>>>>
>>>>
>>>>
>>>>> 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
>>>>>
>>>>>
>>>>>
>>>>>> 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
>>>>>> 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
>>>>>>
>>>>>>
>>>>>>
>>>>
BG
Bruce Griffiths
Sat, Feb 6, 2010 10:48 PM
A round robin test where a couple of well characterised oscillators are
passed around for intercomparison is perhaps the ideal method of
evaluating such effects.
Bruce
WarrenS wrote:
Bob
So, if your point is that there are other ways to do it. ...We Agree
(And the reason for the advanced methods is so that the counter
resolution is not the limiting factor)
Or are you saying a Tight Phase-Lock Loop" is not the simplest and
cheapest way to get 1e13 resolution at 1 sec?
That I'd have to see something new to believe it.
Just so things do not get too far off the original topic, here is a
reminder:
"I would appreciate any comments or observations on the SIMPLEST
scheme for making stability measurements at 1e-13 in one sec."
ws Answer) Try the "Tight Phase-Lock Loop Method"
May want to compare the blocks and equipment needed for A straight
heterodyne system, or a DMTD, compared to the Analog "Tight Phase-Lock
Loop" Method, AND then see what added problems there are because of
injection locking, Osc coupling, Phase noise, ETC, ETC.
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 2:03 PM
Subject: Re: [time-nuts] ADEV vs MDEV
Hi
A straight heterodyne system will get you to the floor of most 10811's
with a very simple (2 stage) limiter.
As with the DMTD, the counter requirements aren't really all that severe.
Bob
On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
"It's possible / likely for injection lock ... to be a problem ..."
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.
"then a part in 10^14 is going to be at the 100 of nanovolts level."
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:
"There is no perfect way to do any of this, only a lot of
compromises ... you need to watch out for".
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
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
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
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
A round robin test where a couple of well characterised oscillators are
passed around for intercomparison is perhaps the ideal method of
evaluating such effects.
Bruce
WarrenS wrote:
> Bob
>
> So, if your point is that there are other ways to do it. ...We Agree
> (And the reason for the advanced methods is so that the counter
> resolution is not the limiting factor)
>
> Or are you saying a Tight Phase-Lock Loop" is not the simplest and
> cheapest way to get 1e13 resolution at 1 sec?
> That I'd have to see something new to believe it.
>
> Just so things do not get too far off the original topic, here is a
> reminder:
>>>>> "I would appreciate any comments or observations on the SIMPLEST
>>>>> scheme for making stability measurements at 1e-13 in one sec."
> ws Answer) Try the "Tight Phase-Lock Loop Method"
>
> May want to compare the blocks and equipment needed for A straight
> heterodyne system, or a DMTD, compared to the Analog "Tight Phase-Lock
> Loop" Method, AND then see what added problems there are because of
> injection locking, Osc coupling, Phase noise, ETC, ETC.
>
>
> 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 2:03 PM
> Subject: Re: [time-nuts] ADEV vs MDEV
>
>
> Hi
>
> A straight heterodyne system will get you to the floor of most 10811's
> with a very simple (2 stage) limiter.
> As with the DMTD, the counter requirements aren't really all that severe.
>
> Bob
> *********************
>
> On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
>
>>
>>> "It's possible / likely for injection lock ... to be a problem ..."
>> 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.
>>
>>> "then a part in 10^14 is going to be at the 100 of nanovolts level."
>> 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:
>>> "There is no perfect way to do any of this, only a lot of
>>> compromises ... you need to watch out for".
>> 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
>>
>>
>>> 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
>>>
>>>>
>>>> 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
>>>> 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
BG
Bruce Griffiths
Sat, Feb 6, 2010 11:12 PM
If one has a high end sound card then it could be used to implement the
bandpass filter and replace the zero crossing detector.
It may be necessary to insert a pilot tone to calibrate the sound card
sampling clock frequency.
A noise floor of about 1E-13/Tau should be achievable.
This simplifies the DMTD system by replacing the zero crossing detector
with a low gain linear preamp.
If one analyses the resultant data off line then one can also try out
different techniques such as a Costas receiver rather than a simple
bandpass filter plus zero crossing detector.
However 1000 seconds of data for 2 channels of 24 bit samples at 192KSPS
will result in a file with a size of at least 1.15GB.
Bruce
Bruce Griffiths wrote:
If one were to use a bandpass filter with a Q of 10 to filter the beat
frequency output of the mixer, then if the input frequency is 10MHz
and the filter component tempco is 100ppm/C then the resultant phase
shift tempco is about 16ps/C referred to the mixer input frequency.
This phase shift tempco is certainly low enough not to have
significant impact when measuring the frequency stability of a typical
10811A if the temperature fluctuations are kept small enough during
the run.
The effect of using a bandpass filter with too narrow a bandwidth is
to artificially reduce ADEV for small Tau, so it may be prudent to use
a higher beat frequency that 1Hz or even 10Hz and not calculate ADEV
for Tau less than say 10(??) times the beat frequency period. A trade
off between this and the effect of aliasing is required.
Bruce
Bob Camp wrote:
Hi
With most 10811 range oscillators the impact of a simple bandpass
filter is low enough to not be a major issue. That's for normal lab
temperatures with the circuitry in a conventional die cast box. No
guarantee if you open the window and let the fresh air blow in during
the run.
That's true with a heterodyne. I can see no obvious reason it would
not be true on DMTD.
Bob
On Feb 6, 2010, at 5:12 PM, Bruce Griffiths wrote:
The only major issue with DMTD systems is that they undersample the
phase fluctuations and hence are subject to aliasing effects.
The low pass filter has to have a bandwidth of the same order as the
beat frequency or the beat frequency signal will be significantly
attenuated.
Since the phase is only sampled once per beat frequency period the
phase fluctuations are undersampled.
Various attempts to use both zero crossings have not been successful.
In principle if one can overcome the increased phase shift tempco
associated with a bandpass filter, using a bandpass filter can in
principle ensure that the phase fluctuations are oversampled.
Bruce
Bob Camp wrote:
Hi
A straight heterodyne system will get you to the floor of most
10811's with a very simple (2 stage) limiter. As with the DMTD, the
counter requirements aren't really all that severe.
Bob
On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
"It's possible / likely for injection lock ... to be a problem ..."
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.
"then a part in 10^14 is going to be at the 100 of nanovolts level."
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:
"There is no perfect way to do any of this, only a lot of
compromises ... you need to watch out for".
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
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
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
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
If one has a high end sound card then it could be used to implement the
bandpass filter and replace the zero crossing detector.
It may be necessary to insert a pilot tone to calibrate the sound card
sampling clock frequency.
A noise floor of about 1E-13/Tau should be achievable.
This simplifies the DMTD system by replacing the zero crossing detector
with a low gain linear preamp.
If one analyses the resultant data off line then one can also try out
different techniques such as a Costas receiver rather than a simple
bandpass filter plus zero crossing detector.
However 1000 seconds of data for 2 channels of 24 bit samples at 192KSPS
will result in a file with a size of at least 1.15GB.
Bruce
Bruce Griffiths wrote:
> If one were to use a bandpass filter with a Q of 10 to filter the beat
> frequency output of the mixer, then if the input frequency is 10MHz
> and the filter component tempco is 100ppm/C then the resultant phase
> shift tempco is about 16ps/C referred to the mixer input frequency.
>
> This phase shift tempco is certainly low enough not to have
> significant impact when measuring the frequency stability of a typical
> 10811A if the temperature fluctuations are kept small enough during
> the run.
>
> The effect of using a bandpass filter with too narrow a bandwidth is
> to artificially reduce ADEV for small Tau, so it may be prudent to use
> a higher beat frequency that 1Hz or even 10Hz and not calculate ADEV
> for Tau less than say 10(??) times the beat frequency period. A trade
> off between this and the effect of aliasing is required.
>
> Bruce
>
> Bob Camp wrote:
>> Hi
>>
>> With most 10811 range oscillators the impact of a simple bandpass
>> filter is low enough to not be a major issue. That's for normal lab
>> temperatures with the circuitry in a conventional die cast box. No
>> guarantee if you open the window and let the fresh air blow in during
>> the run.
>>
>> That's true with a heterodyne. I can see no obvious reason it would
>> not be true on DMTD.
>>
>> Bob
>>
>>
>> On Feb 6, 2010, at 5:12 PM, Bruce Griffiths wrote:
>>
>>> The only major issue with DMTD systems is that they undersample the
>>> phase fluctuations and hence are subject to aliasing effects.
>>> The low pass filter has to have a bandwidth of the same order as the
>>> beat frequency or the beat frequency signal will be significantly
>>> attenuated.
>>> Since the phase is only sampled once per beat frequency period the
>>> phase fluctuations are undersampled.
>>> Various attempts to use both zero crossings have not been successful.
>>>
>>> In principle if one can overcome the increased phase shift tempco
>>> associated with a bandpass filter, using a bandpass filter can in
>>> principle ensure that the phase fluctuations are oversampled.
>>>
>>>
>>> Bruce
>>>
>>> Bob Camp wrote:
>>>> Hi
>>>>
>>>> A straight heterodyne system will get you to the floor of most
>>>> 10811's with a very simple (2 stage) limiter. As with the DMTD, the
>>>> counter requirements aren't really all that severe.
>>>>
>>>> Bob
>>>>
>>>>
>>>> On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
>>>>
>>>>
>>>>>
>>>>>> "It's possible / likely for injection lock ... to be a problem ..."
>>>>>>
>>>>> 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.
>>>>>
>>>>>
>>>>>> "then a part in 10^14 is going to be at the 100 of nanovolts level."
>>>>>>
>>>>> 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:
>>>>>
>>>>>> "There is no perfect way to do any of this, only a lot of
>>>>>> compromises ... you need to watch out for".
>>>>>>
>>>>> 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
>>>>>
>>>>>
>>>>>
>>>>>> 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
>>>>>>
>>>>>>
>>>>>>> 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
>>>>>>> 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
>>>>>>>
>>>>>>>
BC
Bob Camp
Sat, Feb 6, 2010 11:23 PM
Hi
Here's my heterodyne vs tight loop logic:
- With a heterodyne at around 8 Hz your isolation amplifiers are not as critical. Injection locking is a lot less likely at 8 Hz than dead on frequency.
- You eliminate the need for any form of phase lock.
- You do need a mixer and a couple of OP-27/37's.
- Resistors, capacitors, power supplies are likely the same between the two.
- For time tagging you'll need a picket fence source - not much money there. You could also decide not to time tag.
So far the Hetrodyne is as cheap as the tight lock. Probably a bit cheaper. Most of the parts are the same between the two setups, they simply get wired differently.
The only real question is weather your DVM or my junk counter cost more money. My counter can be pretty bad and still not "get in the way". My old (and long gone) Beckman EPUT meter could probably handle the task. Tough to get data out of a vacuum tube counter though.
Most 10811's are not 1x10^-13 at 1 second. A few might be. The vast majority are up around 0.8 to 2x10^-12 at one second. They were only specified to make 5x10^-12 at one second. Both systems are equally limited by the performance of the reference oscillator.
Bob
On Feb 6, 2010, at 5:42 PM, WarrenS wrote:
Bob
So, if your point is that there are other ways to do it. ...We Agree
(And the reason for the advanced methods is so that the counter resolution is not the limiting factor)
Or are you saying a Tight Phase-Lock Loop" is not the simplest and cheapest way to get 1e13 resolution at 1 sec?
That I'd have to see something new to believe it.
Just so things do not get too far off the original topic, here is a reminder:
"I would appreciate any comments or observations on the SIMPLEST scheme for making stability measurements at 1e-13 in one sec."
ws Answer) Try the "Tight Phase-Lock Loop Method"
May want to compare the blocks and equipment needed for A straight heterodyne system, or a DMTD, compared to the Analog "Tight Phase-Lock Loop" Method, AND then see what added problems there are because of injection locking, Osc coupling, Phase noise, ETC, ETC.
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 2:03 PM
Subject: Re: [time-nuts] ADEV vs MDEV
Hi
A straight heterodyne system will get you to the floor of most 10811's with a very simple (2 stage) limiter.
As with the DMTD, the counter requirements aren't really all that severe.
Bob
On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
"It's possible / likely for injection lock ... to be a problem ..."
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.
"then a part in 10^14 is going to be at the 100 of nanovolts level."
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:
"There is no perfect way to do any of this, only a lot of compromises ... you need to watch out for".
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
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
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
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
Here's my heterodyne vs tight loop logic:
1) With a heterodyne at around 8 Hz your isolation amplifiers are not as critical. Injection locking is a lot less likely at 8 Hz than dead on frequency.
2) You eliminate the need for any form of phase lock.
3) You do need a mixer and a couple of OP-27/37's.
4) Resistors, capacitors, power supplies are likely the same between the two.
5) For time tagging you'll need a picket fence source - not much money there. You could also decide not to time tag.
So far the Hetrodyne is as cheap as the tight lock. Probably a bit cheaper. Most of the parts are the same between the two setups, they simply get wired differently.
The only real question is weather your DVM or my junk counter cost more money. My counter can be pretty bad and still not "get in the way". My old (and long gone) Beckman EPUT meter could probably handle the task. Tough to get data out of a vacuum tube counter though.
Most 10811's are not 1x10^-13 at 1 second. A few might be. The vast majority are up around 0.8 to 2x10^-12 at one second. They were only specified to make 5x10^-12 at one second. Both systems are equally limited by the performance of the reference oscillator.
Bob
On Feb 6, 2010, at 5:42 PM, WarrenS wrote:
> Bob
>
> So, if your point is that there are other ways to do it. ...We Agree
> (And the reason for the advanced methods is so that the counter resolution is not the limiting factor)
>
> Or are you saying a Tight Phase-Lock Loop" is not the simplest and cheapest way to get 1e13 resolution at 1 sec?
> That I'd have to see something new to believe it.
>
> Just so things do not get too far off the original topic, here is a reminder:
>>>>> "I would appreciate any comments or observations on the SIMPLEST scheme for making stability measurements at 1e-13 in one sec."
> ws Answer) Try the "Tight Phase-Lock Loop Method"
>
> May want to compare the blocks and equipment needed for A straight heterodyne system, or a DMTD, compared to the Analog "Tight Phase-Lock Loop" Method, AND then see what added problems there are because of injection locking, Osc coupling, Phase noise, ETC, ETC.
>
>
> 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 2:03 PM
> Subject: Re: [time-nuts] ADEV vs MDEV
>
>
> Hi
>
> A straight heterodyne system will get you to the floor of most 10811's with a very simple (2 stage) limiter.
> As with the DMTD, the counter requirements aren't really all that severe.
>
> Bob
> *********************
>
> On Feb 6, 2010, at 4:24 PM, WarrenS wrote:
>
>>
>>> "It's possible / likely for injection lock ... to be a problem ..."
>> 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.
>>
>>> "then a part in 10^14 is going to be at the 100 of nanovolts level."
>> 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:
>>> "There is no perfect way to do any of this, only a lot of compromises ... you need to watch out for".
>> 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
>>
>>
>>> 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
>>>
>>>>
>>>> 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
>>>> 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
>>>>
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
>
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
W
WarrenS
Sat, Feb 6, 2010 11:27 PM
And still another way of looking at the problem is:
One wants to know the Average freq over each of the 1 sec Tau sample
intervals,
and do it in such a way that there is no dead spots and no overlapping
information. (within the stated bandwidth)
Can be done with Phase (which tends to have limited resolution at low tau)
BUT Easy enough to do with a properly set up "Tight Phase-Lock Loop".
Now send that raw data to "PLOTTER" and tell it that it is Freq data and let
it do its thing.
NO phase need be involved at the raw data, and I don't think 'Plotter' is
first turning Freq Data into phase to get ADEV Freq data.
but that is a Ulrich question.
"However its easier just to use the sampled phases in the alternative
formula."
Are we off topic again?
For me, It is just as easy to have "Plotter" use either formula, It does not
complain about which is harder.
BTW, using a ADEV program I wrote in excel. When using Freq data, it was a
little easer than using Phase data.
Both give the same answer, If there is enough accurate Phase resolution, i.e
0.1 pS. for low taus faster than 1 sec.
"One cannot use EFC samples spaced at intervals of Tau directly ..."
Right, I hope all know that. Needs to be integrated (averaged) Freq over the
sampled Tau period,
NOT instantaneous freq at some random points along the way.
The NIST VtoF converter did that integration and so will a simple RC filter
with oversampling and a PC.
Still don't see where it needs to reconstruct the Phase evolution.
On the contrary the phase is used to reconstruct the Average Freq.
AND one of the BIG problems is that is very hard to do accurately if a Phase
TI is being used at Taus below 100 ms. (10Hz)
Just so things do not get too far off the original topic, here is a
reminder:
"I would appreciate any comments or observations on the SIMPLEST scheme
for making stability measurements at 1e-13 in one sec."
ws
----- Original Message -----
From: "Bruce Griffiths" bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, February 06, 2010 2:24 PM
Subject: Re: [time-nuts] ADEV vs MDEV
Another way of looking at the problem is:
One has to reconstruct the phase evolution with time by integrating the
instantaneous frequency.
Then if the resultant phase evolution is sampled every Tau seconds and the
first differences taken and divided by Tau the result is a sequence of
average frequency samples required by the AVAR formula.
However its easier just to use the sampled phases in the alternative
formula.
With the tight PLL method one has a sequence of frequency samples averaged
over an interval on the order of the inverse PLL loop bandwidth.
One then has to use these samples to reconstruct the phase evolution over
time.
One cannot use EFC samples spaced at intervals of Tau directly in the ADEV
formula which requires a sequence of frequency averages over an interval
of Tau.
If one ignores this requirement the resultant stability measure is not
ADEV.
Bruce
Bruce Griffiths wrote:
The tight PLL method doesn't directly produce the average frequency over
Tau.
As explained in (see snapshot of relevant section):
NIST special Publication 1065 Handbook of Frequency Stability Analysis
http://tf.nist.gov/timefreq/general/pdf/2220.pdf
the average frequency deviations for averaging time Tau are needed for
the calculation.
You need to sample at a sufficiently high rate to avoid aliasing and
average (ie integrate) the individual EFC samples.
If one uses phase measures then the fluctuations in the frequency
averages can easily and directly calculated from the difference between
the phase measured at time intervals separated by Tau.
Bruce
WarrenS wrote:
Thus NIST and others quietly dropped this method several decades ago.
Could it be another reason?
I'll bet that was after they wanted to do better than 1e14 resolution
AND had unlimited amounts of time and Money,
Something most time Nuts are not blessed with. I Never said it was the
BEST way.
JUST given the goal, which was 1e13 in one second, there is not a
simpler and cheaper way to do it.
And nothing you said counter that point.
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.
Well ONE of us certainly has something backward.
To calculate ADEV, MDEV etc. YOU need Freq Differences.
The first thing that happens when phase is used is that it is turned
into Freq by taking the difference between each sample.
Integrated Freq data, which is what "Tight Phase-Lock Loop Method" gives
you directly (no Phase conversion needed),
Need not FIRST turned into Phase so that it can then be turned back into
Freq.
BUT in any case there is no difference in the noise, for a given
bandwidth, If you don't run out of digits and You have enough
resolution.
The "Tight Phase-Lock Loop Method" can EASY get sub pS resolution, which
is better than most other ways.
AND don't need filters and slue rate control and multistage limiters and
on & on to do it, an RC works fine to replace all the stuff.
ws
----- Original Message ----- From: "Bruce Griffiths"
bruce.griffiths@xtra.co.nz
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, February 06, 2010 12:11 PM
Subject: Re: [time-nuts] ADEV vs MDEV
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:
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
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
And still another way of looking at the problem is:
One wants to know the Average freq over each of the 1 sec Tau sample
intervals,
and do it in such a way that there is no dead spots and no overlapping
information. (within the stated bandwidth)
Can be done with Phase (which tends to have limited resolution at low tau)
BUT Easy enough to do with a properly set up "Tight Phase-Lock Loop".
Now send that raw data to "PLOTTER" and tell it that it is Freq data and let
it do its thing.
NO phase need be involved at the raw data, and I don't think 'Plotter' is
first turning Freq Data into phase to get ADEV Freq data.
but that is a Ulrich question.
> "However its easier just to use the sampled phases in the alternative
> formula."
Are we off topic again?
For me, It is just as easy to have "Plotter" use either formula, It does not
complain about which is harder.
BTW, using a ADEV program I wrote in excel. When using Freq data, it was a
little easer than using Phase data.
Both give the same answer, If there is enough accurate Phase resolution, i.e
0.1 pS. for low taus faster than 1 sec.
> "One cannot use EFC samples spaced at intervals of Tau directly ..."
Right, I hope all know that. Needs to be integrated (averaged) Freq over the
sampled Tau period,
NOT instantaneous freq at some random points along the way.
The NIST VtoF converter did that integration and so will a simple RC filter
with oversampling and a PC.
Still don't see where it needs to reconstruct the Phase evolution.
On the contrary the phase is used to reconstruct the Average Freq.
AND one of the BIG problems is that is very hard to do accurately if a Phase
TI is being used at Taus below 100 ms. (10Hz)
Just so things do not get too far off the original topic, here is a
reminder:
>>>> "I would appreciate any comments or observations on the SIMPLEST scheme
>>>> for making stability measurements at 1e-13 in one sec."
ws
**************
----- Original Message -----
From: "Bruce Griffiths" <bruce.griffiths@xtra.co.nz>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Saturday, February 06, 2010 2:24 PM
Subject: Re: [time-nuts] ADEV vs MDEV
> Another way of looking at the problem is:
> One has to reconstruct the phase evolution with time by integrating the
> instantaneous frequency.
> Then if the resultant phase evolution is sampled every Tau seconds and the
> first differences taken and divided by Tau the result is a sequence of
> average frequency samples required by the AVAR formula.
> However its easier just to use the sampled phases in the alternative
> formula.
>
> With the tight PLL method one has a sequence of frequency samples averaged
> over an interval on the order of the inverse PLL loop bandwidth.
> One then has to use these samples to reconstruct the phase evolution over
> time.
>
> One cannot use EFC samples spaced at intervals of Tau directly in the ADEV
> formula which requires a sequence of frequency averages over an interval
> of Tau.
> If one ignores this requirement the resultant stability measure is not
> ADEV.
>
> Bruce
>
> Bruce Griffiths wrote:
>> The tight PLL method doesn't directly produce the average frequency over
>> Tau.
>> As explained in (see snapshot of relevant section):
>> NIST special Publication 1065 Handbook of Frequency Stability Analysis
>> <http://tf.nist.gov/timefreq/general/pdf/2220.pdf>
>> the average frequency deviations for averaging time Tau are needed for
>> the calculation.
>> You need to sample at a sufficiently high rate to avoid aliasing and
>> average (ie integrate) the individual EFC samples.
>>
>> If one uses phase measures then the fluctuations in the frequency
>> averages can easily and directly calculated from the difference between
>> the phase measured at time intervals separated by Tau.
>>
>> Bruce
>>
>> WarrenS wrote:
>>> Bruce said:
>>>
>>>> Thus NIST and others quietly dropped this method several decades ago.
>>> Could it be another reason?
>>> I'll bet that was after they wanted to do better than 1e14 resolution
>>> AND had unlimited amounts of time and Money,
>>> Something most time Nuts are not blessed with. I Never said it was the
>>> BEST way.
>>> JUST given the goal, which was 1e13 in one second, there is not a
>>> simpler and cheaper way to do it.
>>> And nothing you said counter that point.
>>>
>>>
>>>> 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.
>>>
>>> Well ONE of us certainly has something backward.
>>> To calculate ADEV, MDEV etc. YOU need Freq Differences.
>>> The first thing that happens when phase is used is that it is turned
>>> into Freq by taking the difference between each sample.
>>> Integrated Freq data, which is what "Tight Phase-Lock Loop Method" gives
>>> you directly (no Phase conversion needed),
>>> Need not FIRST turned into Phase so that it can then be turned back into
>>> Freq.
>>> BUT in any case there is no difference in the noise, for a given
>>> bandwidth, If you don't run out of digits and You have enough
>>> resolution.
>>> The "Tight Phase-Lock Loop Method" can EASY get sub pS resolution, which
>>> is better than most other ways.
>>> AND don't need filters and slue rate control and multistage limiters and
>>> on & on to do it, an RC works fine to replace all the stuff.
>>>
>>> ws
>>>
>>> *****************
>>>
>>> ----- Original Message ----- From: "Bruce Griffiths"
>>> <bruce.griffiths@xtra.co.nz>
>>> To: "Discussion of precise time and frequency measurement"
>>> <time-nuts@febo.com>
>>> Sent: Saturday, February 06, 2010 12:11 PM
>>> Subject: Re: [time-nuts] ADEV vs MDEV
>>>
>>>
>>>> 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:
>>>>>
>>>>>> 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
>>>>> 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
>>>>>
>>>>>
>>>>>
>
>
>
>
>
