Re: [time-nuts] What is the best counter for a Time Nuts?

[Mike Monett]

  "Tom Van Baak" <[EMAIL PROTECTED]> wrote:

  >> 24 hrs  would get you to 2.77e-10 / (24 * 3600) =  3.2e-15, which
  >> is very acceptable. That puts you in the big leagues.

  >Hi Mike,

  > It doesn't  quite work this way. If it did, hey, you could  wait a
  > month, and be better than the big leagues!

  > The missing consideration is the stability of the test  setup. The
  > frequency reference  and the phase comparator would  have  to have
  > 10^-15 levels  of  stability before you could claim  this  sort of
  > per-day measurement resolution. I can tell you a  telecom rubidium
  > and hp3575A are not even close to this.

  I know. All I was saying is he could resolve a  frequency difference
  of 3.2e-15 in 24 hours. That is big league stuff.

  As you  point  out, that is far better than  the  oscillators  he is
  using. So  his  method  is valid, and his  equipment  is  capable of
  making useful  and important measurements. Since it is  a completely
  different method, it would give a valuable cross-check against other
  methods.

  As far as the measurement stability, the phase measurement is merely
  measuring the  time between two signals. I would expect  HP  to hold
  much better than 0.1 degree with no problems. Since it  is measuring
  a relatively small change and not an absolute value,  the resolution
  of 0.1 degree could be considered valid data.

  So his equipment is capable of resolving a frequency difference that
  is much smaller than the stability of the oscillators. That is good.

  But we don't know what would happen during a 24 hour run. So  what I
  was hoping for was a table of phase angle measurements perhaps every
  15 minutes for the first several hours to get a feeling for  the ups
  and downs  of the phase angle drift, then perhaps every  hour  for a
  couple of days. That would be very valuable data.

  >> Can you see any drift in the GPS time?

  > You're not  likely  to see "drift in GPS time" when  using  a free
  > running rubidium or another GPSDO as a reference. Do you see why?

  Sorry, badly  worded. I thought he locked the rubidium  to  gps, and
  was wondering  if he monitored the DC error to the rubidium,  and if
  he saw any diurnal change.

  If so, that would indicate the rubidium is quite stable by itself.

  >/tvb

  Best Regards,

  Mike Monett

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Tom Van Baak]

> This seems like a pretty straight forward technique. Am  I missing
> something?

Hi Charlie,

Nope, your basic method of measuring frequency *accuracy*
with two phase angle measurements is fine. I think many of us
do the same, one way or another. Relative frequency error is,
after all, just a measure of _phase_ drift over time. So you're
good to go.

One has to be careful, though, not to claim more accuracy than
is fair. Once you take into account
the instability of your unit under test,
the resolution and stability of the phase comparator itself,
and the accuracy and stability of the frequency reference,
you may find that your accuracy method is slightly less precise
than the simple math suggests.

Going one step further, note that measuring frequency *stability* 
is essentially taking multiple frequency accuracy measurements
and statistically looking at _frequency_ drift over time.

>  24 hrs  would get you to 2.77e-10 / (24 * 3600) = 3.2e-15,  which is
>  very acceptable. That puts you in the big leagues.

Hi Mike,

It doesn't quite work this way. If it did, hey, you could wait a
month, and be better than the big leagues!

The missing consideration is the stability of the test setup. The
frequency reference and the phase comparator would have to
have 10^-15 levels of stability before you could claim this sort
of per-day measurement resolution. I can tell you a telecom
rubidium and hp3575A are not even close to this.

>  Can you see any drift in the GPS time?

You're not likely to see "drift in GPS time" when using a free
running rubidium or another GPSDO as a reference. Do you
see why?

/tvb



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Re: [time-nuts] What is the best counter for a Time Nuts?

[Mike Monett]

  Hello Charlie,

  I am  very pleased to see your post. Measurements and good  data are
  very important, and much more valuable than handwaving.

  "Myers, Charlie" <[EMAIL PROTECTED]> wrote:

  >  Hello to the Time Nuts,

  > I have been reading the mail on this topic for the last week or so
  > with great interest. Lots of interesting ideas have been put forth
  > for measuring  frequency  to a high degree  of  precision  and for
  > comparing a  10 MHz clock's frequency to a  highly  accurate 10Mhz
  > frequency "standard".

  > The way I measure the frequency of a 10 MHz clock is to compare it
  > to a second 10MHz clock of known accuracy and stability,  not only
  > with a frequency counter but also with a phase meter.

  This is excellent procedure. Cross-checking is always a good idea. I
  try to  find as many ways to measure something as  possible.  If one
  measurement doesn't  agree  with the others, it  shows  something is
  wrong somewhere. So this is not a boring or stupid waste of time. It
  is essential.

  > I have  several  GPS   disciplined   OCXO's,  one  GPS disciplined
  > Rubidiumoscillator,   and   several   free   running  rubidium
  > oscillators. I  measure the frequency of an unknown  10  MHz clock
  > using a 2 step process.

  What are  the models? What GPS card are you using, and  how  are you
  locking to it?

  > First I  measure  the  unknown  10 MHz  clock  using  an  HP 5384A
  > reciprocal counter  that  employs  my known 10  MHz  clock  as its
  > external timebase.  I  set  the gate time to  10  seconds  and the
  > counter delivers a frequency measurement with a resolution of less
  > than 3 mhz (3 millihertz).

  Do you  happen  to know any source for the manual?  There  is almost
  nothing on the web.

  > So, assuming my known timebase is "bang on", I know  the frequency
  > of the unknown 10 MHz source to an accuracy of roughly 3e-10  or 3
  > parts in 10 billion.

  > To get  a  more precise measurement  of  the  frequency difference
  > between the two 10 MHz clocks, I supply the known 10 MHz  clock to
  > the Channel  A  input  of an HP  3575A  Gain-Phase  meter  and the
  > unknown 10  MHz  clock to the channel B  input  of  the Gain-Phase
  > meter.

  Another very  difficult instrument to find any data on.  The  best I
  could find shows it has an accuracy of +/- 0.5 degree and resolution
  of 0.1 degree.

  I think in this case the resolution parameter might be quite valid.

  You are  measuring a small change, not an absolute value.  So  if it
  stable, I'd consider keeping it.

  > I measure the change in the phase angle between the 2 input clocks
  > over some convenient time interval (eg, 10, 100, or 1,000 seconds)
  > and compute the frequency difference using the formula:

  > Frequency Difference  =  [Change  in Phase  Angle  (in  degrees) /
  > Measurement Duration (in seconds)] X [1 / 360]

  > The frequency  difference  can   then  be  converted  to frequency
  > accuracy using the formula:

  >  Accuracy = Frequency Difference / 1e7

  > This seems like a pretty straight forward technique. Am  I missing
  > something?

  >  Charlie Myers
  >  WA3RAD

  Charlie, this could be quite significant. A cross-check on your math
  shows 1  degree  at  10MHz  is   1e-7  /  360  =  2.77e-10s,  or 277
  picoseconds. That's not bad at all.

  In 1000 seconds, you could resolve 2.77e-10 / 1e3 = 2.77e-13. That's
  pretty good.  1000  seconds  is only 16.6  minutes,  which  is quite
  reasonable. And that's truncating the resolution to 1 degree.

  24 hrs  would get you to 2.77e-10 / (24 * 3600) = 3.2e-15,  which is
  very acceptable. That puts you in the big leagues.

  Now comes the big question - what kind of data do you get?

  Can you give some examples of the measurements you have made?

  Can you see any drift in the GPS time?

  Thanks again very much for your post!

  Best Regards,

  Mike Monett

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Steve Rooke]

2008/10/12 Bruce Griffiths <[EMAIL PROTECTED]>:
> Steve Rooke wrote:
>> 2008/10/12 Myers, Charlie <[EMAIL PROTECTED]>:
>>
>>> Hello to the Time Nuts,
>>>
>>> I have been reading the mail on this topic for the last week or so with
>>> great interest.  Lots of interesting ideas have been put forth for
>>> measuring frequency to a high degree of precision and for comparing a 10
>>> MHz clock's frequency to a highly accurate 10Mhz frequency "standard".
>>>
>>> The way I measure the frequency of a 10 MHz clock is to compare it to a
>>> second 10MHz clock of known accuracy and stability, not only with a
>>> frequency counter but also with a phase meter.
>>>
>>> I have several GPS disciplined OCXO's, one GPS disciplined Rubidium
>>> oscillator, and several free running rubidium oscillators.  I measure
>>> the frequency of an unknown 10 MHz clock using a 2 step process.  First
>>> I measure the unknown 10 MHz clock using an HP 5384A reciprocal counter
>>> that employs my known 10 MHz clock as its external timebase.  I set the
>>> gate time to 10 seconds and the counter delivers a frequency measurement
>>> with a resolution of less than 3 mhz (3 millihertz).  So, assuming my
>>> known timebase is "bang on", I know the frequency of the unknown 10 MHz
>>> source to an accuracy of roughly 3e-10 or 3 parts in 10 billion.
>>>
>>> To get a more precise measurement of the frequency difference between
>>> the two 10 MHz clocks, I supply the known 10 MHz clock to the Channel A
>>> input of an HP 3575A Gain-Phase meter and the unknown 10 MHz clock to
>>> the channel B input of the Gain-Phase meter.  I measure the change in
>>> the phase angle between the 2 input clocks over some convenient time
>>> interval (e.g., 10, 100, or 1,000 seconds) and compute the frequency
>>> difference using the formula:
>>>
>>>
>>> Frequency Difference = [Change in Phase Angle (in degrees) / Measurement
>>> Duration (in seconds)] X [1 / 360]
>>>
>>> The frequency difference can then be converted to frequency accuracy
>>> using the formula:
>>>
>>> Accuracy = Frequency Difference / 1e7
>>>
>>>
>>> This seems like a pretty straight forward technique.  Am I missing
>>> something?
>>>
>>
>> So what's time nutty about this method...
>>
>> :)
>>
> Using ~40 year old boat anchor rackmount equipment to measure something
> that can be done more accurately with a handful Of ICs.

That would surely just make it nutty then...
-- 
Steve Rooke - ZL3TUV & G8KVD
Omnium finis imminet

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Steve Rooke wrote:
> 2008/10/12 Myers, Charlie <[EMAIL PROTECTED]>:
>   
>> Hello to the Time Nuts,
>>
>> I have been reading the mail on this topic for the last week or so with
>> great interest.  Lots of interesting ideas have been put forth for
>> measuring frequency to a high degree of precision and for comparing a 10
>> MHz clock's frequency to a highly accurate 10Mhz frequency "standard".
>>
>> The way I measure the frequency of a 10 MHz clock is to compare it to a
>> second 10MHz clock of known accuracy and stability, not only with a
>> frequency counter but also with a phase meter.
>>
>> I have several GPS disciplined OCXO's, one GPS disciplined Rubidium
>> oscillator, and several free running rubidium oscillators.  I measure
>> the frequency of an unknown 10 MHz clock using a 2 step process.  First
>> I measure the unknown 10 MHz clock using an HP 5384A reciprocal counter
>> that employs my known 10 MHz clock as its external timebase.  I set the
>> gate time to 10 seconds and the counter delivers a frequency measurement
>> with a resolution of less than 3 mhz (3 millihertz).  So, assuming my
>> known timebase is "bang on", I know the frequency of the unknown 10 MHz
>> source to an accuracy of roughly 3e-10 or 3 parts in 10 billion.
>>
>> To get a more precise measurement of the frequency difference between
>> the two 10 MHz clocks, I supply the known 10 MHz clock to the Channel A
>> input of an HP 3575A Gain-Phase meter and the unknown 10 MHz clock to
>> the channel B input of the Gain-Phase meter.  I measure the change in
>> the phase angle between the 2 input clocks over some convenient time
>> interval (e.g., 10, 100, or 1,000 seconds) and compute the frequency
>> difference using the formula:
>>
>>
>> Frequency Difference = [Change in Phase Angle (in degrees) / Measurement
>> Duration (in seconds)] X [1 / 360]
>>
>> The frequency difference can then be converted to frequency accuracy
>> using the formula:
>>
>> Accuracy = Frequency Difference / 1e7
>>
>>
>> This seems like a pretty straight forward technique.  Am I missing
>> something?
>> 
>
> So what's time nutty about this method...
>
> :)
>   
Using ~40 year old boat anchor rackmount equipment to measure something 
that can be done more accurately with a handful Of ICs.

Bruce

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Steve Rooke]

2008/10/12 Myers, Charlie <[EMAIL PROTECTED]>:
> Hello to the Time Nuts,
>
> I have been reading the mail on this topic for the last week or so with
> great interest.  Lots of interesting ideas have been put forth for
> measuring frequency to a high degree of precision and for comparing a 10
> MHz clock's frequency to a highly accurate 10Mhz frequency "standard".
>
> The way I measure the frequency of a 10 MHz clock is to compare it to a
> second 10MHz clock of known accuracy and stability, not only with a
> frequency counter but also with a phase meter.
>
> I have several GPS disciplined OCXO's, one GPS disciplined Rubidium
> oscillator, and several free running rubidium oscillators.  I measure
> the frequency of an unknown 10 MHz clock using a 2 step process.  First
> I measure the unknown 10 MHz clock using an HP 5384A reciprocal counter
> that employs my known 10 MHz clock as its external timebase.  I set the
> gate time to 10 seconds and the counter delivers a frequency measurement
> with a resolution of less than 3 mhz (3 millihertz).  So, assuming my
> known timebase is "bang on", I know the frequency of the unknown 10 MHz
> source to an accuracy of roughly 3e-10 or 3 parts in 10 billion.
>
> To get a more precise measurement of the frequency difference between
> the two 10 MHz clocks, I supply the known 10 MHz clock to the Channel A
> input of an HP 3575A Gain-Phase meter and the unknown 10 MHz clock to
> the channel B input of the Gain-Phase meter.  I measure the change in
> the phase angle between the 2 input clocks over some convenient time
> interval (e.g., 10, 100, or 1,000 seconds) and compute the frequency
> difference using the formula:
>
>
> Frequency Difference = [Change in Phase Angle (in degrees) / Measurement
> Duration (in seconds)] X [1 / 360]
>
> The frequency difference can then be converted to frequency accuracy
> using the formula:
>
> Accuracy = Frequency Difference / 1e7
>
>
> This seems like a pretty straight forward technique.  Am I missing
> something?

So what's time nutty about this method...

:)
-- 
Steve Rooke - ZL3TUV & G8KVD
Omnium finis imminet

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[time-nuts] What is the best counter for a Time Nuts?

[Myers, Charlie]

Hello to the Time Nuts,

I have been reading the mail on this topic for the last week or so with
great interest.  Lots of interesting ideas have been put forth for
measuring frequency to a high degree of precision and for comparing a 10
MHz clock's frequency to a highly accurate 10Mhz frequency "standard".

The way I measure the frequency of a 10 MHz clock is to compare it to a
second 10MHz clock of known accuracy and stability, not only with a
frequency counter but also with a phase meter.  

I have several GPS disciplined OCXO's, one GPS disciplined Rubidium
oscillator, and several free running rubidium oscillators.  I measure
the frequency of an unknown 10 MHz clock using a 2 step process.  First
I measure the unknown 10 MHz clock using an HP 5384A reciprocal counter
that employs my known 10 MHz clock as its external timebase.  I set the
gate time to 10 seconds and the counter delivers a frequency measurement
with a resolution of less than 3 mhz (3 millihertz).  So, assuming my
known timebase is "bang on", I know the frequency of the unknown 10 MHz
source to an accuracy of roughly 3e-10 or 3 parts in 10 billion.  

To get a more precise measurement of the frequency difference between
the two 10 MHz clocks, I supply the known 10 MHz clock to the Channel A
input of an HP 3575A Gain-Phase meter and the unknown 10 MHz clock to
the channel B input of the Gain-Phase meter.  I measure the change in
the phase angle between the 2 input clocks over some convenient time
interval (e.g., 10, 100, or 1,000 seconds) and compute the frequency
difference using the formula:


Frequency Difference = [Change in Phase Angle (in degrees) / Measurement
Duration (in seconds)] X [1 / 360]

The frequency difference can then be converted to frequency accuracy
using the formula:

Accuracy = Frequency Difference / 1e7


This seems like a pretty straight forward technique.  Am I missing
something?



Charlie Myers
WA3RAD


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Re: [time-nuts] What is the best counter for a Time Nuts?

[Mike Monett]

  > Mike

  > You've obviously never tried this, in practice its noise is  a lot
  > higher than you think, perhaps 2 orders of magnitude worse  than a
  > double balanced mixer.

  > You need to breadboard this and do some tests.

  > Bruce

  Bruce,

  Thank you for the reply. Please let me introduce myself.

  I know this circuit very well. I've been using it since  1970, where
  it formed  the  basis  of development work  that  led  to  my second
  patent, US 4533881. Among other things, this patent was the first to
  recognize the  problem  of   deadband   in  the  PLL phase/frequency
  detector, and  shows how to fix it. People still get  it  wrong even
  today.

  That patent led to an amazing discovery, documented in the paper:

  "Effect of  Bitshift   Distribution   on   Error   Rate  in Magnetic
  Recording", Eric R. Katz and Thomas G. Campbell, IEEE Transaction on
  Magnetics, Vol. MAG-15, No. 3, May 1979, pp 1050-1053.

  This technique  saved  the  hard  disk  drive  industry  hundreds of
  millions, if not billions of dollars. It did this by  separating the
  contributions of  the head, media, preamplifier, servo  system, disk
  defects, external  EMI,  and anything else that  affected  the error
  rate. It gave manufacturing a very quick test to tell if a drive was
  meeting the error rate spec, and tells what to do if it failed.

  It also  gave  head  and media manufacturers a  way  to  measure the
  performance of  their  products, and a way to  meet  the competition
  that was  using the same technique. It told R&D  engineers  how well
  their design  was  working, and what to do to improve it.  It  had a
  tremendous effect  on  every disk drive company on  the  planet, and
  there were over 220 at the peak.

  I made a great deal of money developing test systems that  used this
  technique for  manufacturers all over the world. I owned a  house in
  Saratoga Hills in Silicon Valley. I had two Mercedes and three Lexus
  for my  managers,  and gave a bunch of Toyota station  wagons  to my
  staff so they wouldn't have problems getting to work. I  helped most
  of my staff buy houses. I bought this plane brand new,  Piper Malibu
  N4360V.

  http://www.jetphotos.net/viewphoto.php?id=5874208&nseq=0

  This is  a twin turbocharged with constant speed  prop, pressurized,
  retractable, six-place  high  performance  aircraft  with  a service
  ceiling of  25,000 ft. That is above most of the weather, and  I put
  over 750  hours  on it flying to customers all over the  US.  It was
  truly the nicest plane I have ever had the pleasure to fly,  but you
  have to  watch  it on takeoff when the turbos spool  up.  The torque
  will take you into the weeds if you are not ready for it. It is very
  nice to see it is still in the air:)

  All of this resulted from work using the circuit I  described above,
  so I  know it pretty well. It works a lot better than  you  think it
  does.

  It also  forms the basis of two of my latest inventions,  which will
  be disclosed  as soon as I have time to get my new web  site  up and
  running.

  The old  site was finally taken down by Microsoft, so  I  can't give
  you a  working  url. But at this moment,  searching  for  the phrase
  "binary sampler"  in quotes gives me the first four hits  in google,
  so you  can see it was up until recently. Unfortunately  the WayBack
  machine doesn't link to images, so I can't send you there to see how
  it works.  But  I  should  have  the  above  circuit  running around
  Christmas, along with some other new stuff.

  I'll be happy to discuss these issues when there is hardware to make
  measurements on.

  Best Regards,

  Mike Monett

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Mike S]

At 04:17 PM 10/11/2008, Magnus Danielson wrote...
>It's an analogue world after all, so we need to evaluate it as an
>analogue system.

I take it you don't agree with quantum theory (mechanics, 
electrodynamics, chromodynamics, etc.)?

I suppose we're still far from measuring at the scale of Planck time, 
so it's hard to prove one way or the other. Still, quantum physics has 
been empirically useful where analog physics fails. 


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Re: [time-nuts] What is the best counter for a Time Nuts?

[Mike Monett]

  Magnus Danielson <[EMAIL PROTECTED]> wrote:

  [...]

  > It's an analogue world after all, so we need to evaluate it  as an
  > analogue system.

  >Cheers,
  >Magnus

  Magnus,

  Thank you for your reply. I challenge you to a duel.  Picoseconds at
  50 paces:)

  You build  your  system  and  show the  results.  I  should  have my
  complete system running by Christmas, and will post everything.

  Perhaps we can agree on a common set of oscillators. I will  have an
  old LPRO  Rubidium  and two IsoTemp 134 OXCO's from  eBay,  plus GPS
  time.

  Bet I beat you:)

  Best Regards,

  Mike Monett

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Steve Rooke]

2008/10/12 Mike Monett <[EMAIL PROTECTED]>:
>  Two corrections:
>
>  The denominators in the following equations have the  wrong polarity
>  in the exponent:
>
>  > the overall resolution is 1e-7 / 1e-6 = 1e-13.
>
>  This should read:
>
>  > the overall resolution is 1e-7 / 1e+6 = 1e-13.
>
>  Similarly
>
>  > The overall  resolution  in this example would be  1e-8  /  1e-7 =
>  > 1e-15.
>
>  This should read:
>
>  > The overall  resolution  in this example would be  1e-8  /  1e+7 =
>  > 1e-15.
>
>  These were obvious typos that I hope did not confuse anyone.
>
>  Best Regards
>
>  Mike Monett
>
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>

I was confused even before I read the posts :)

73
Steve
-- 
Steve Rooke - ZL3TUV & G8KVD
Omnium finis imminet

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Mike Monett]

  Two corrections: 

  The denominators in the following equations have the  wrong polarity
  in the exponent:

  > the overall resolution is 1e-7 / 1e-6 = 1e-13.

  This should read:

  > the overall resolution is 1e-7 / 1e+6 = 1e-13.

  Similarly

  > The overall  resolution  in this example would be  1e-8  /  1e-7 =
  > 1e-15.

  This should read:

  > The overall  resolution  in this example would be  1e-8  /  1e+7 =
  > 1e-15.

  These were obvious typos that I hope did not confuse anyone.

  Best Regards

  Mike Monett

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Mike Monett wrote:
>   The Allen deviation is used to describe the performance of  a stable
>   clock. Measuring the performance of a good clock requires  a counter
>   with resolution  down  to picosecond levels. As  Dr  Griffith points
>   out, some  modern counters may have internal signal  processing that
>   makes them unsuitable for this task.
>
>   Another thread  discussed using a mixer to  generate  the difference
>   frequency between  two oscillators, then measuring the  stability of
>   the resulting beat note:
>
>   http://www.febo.com/pipermail/time-nuts/2005-July/019006.html
>
>   The basic  principle  is sound. If the oscillators  were  running at
>   10MHz, and  the  frequency difference was 1 Hz, then  the  beat note
>   would be 1 Hz.
>
>   This represents  one  part in 10 million, or  1e-7  of  the original
>   frequency. If  the  beat   note   is   measured  with  1 microsecond
>   resolution, the  overall resolution is 1e-7 / 1e-6 = 1e-13.  This is
>   beyond the capability of most commercial counters.
>
>   The difficulty  with this approach is the output of a mixer is  at a
>   fairly low  level, perhaps 50 millivolts or so. The  frequency would
>   also be very low, perhaps 1 Hz. This means the counter would have to
>   trigger accurately on a very slow-rising, low amplitude signal.
>
>   
Not true, if both the RF and IF ports are saturated as usually 
recommended for phase detector operation, the output can be as high as 
2V pp (e.g. Minicircuits RPD-1).
The solution to the triggering problem with low slew rate input signals 
is simple, build a slope amplifier.
A slope amplifier (in optimised form) consists of a set of cascaded 
limiting amplifiers with gradually increasing gain and bandwidth.
Oliver Collins showed how to optimise the gain and bandwidth 
distribution to minimise the output noise.
I have since generalised his results to include the case where the input 
(self) noise for all amplifiers are not identical.
For further details/references see:
http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html 


I have some spreadsheets for calculating the amplifier parameters both 
for the the restricted and general cases.
>   This is  a very difficult measurement problem. The accuracy  will be
>   degraded by  noise,  such  as the 60Hz  AC  line  frequency  and its
>   harmonics, switching noise from the pc power supplies  and monitors,
>   radiation from nearby fluorescent lighting, plus thermal  noise from
>   the mixer and input stage of the amplifiers.
>
>   This low-level noise is very difficult to eliminate, especially when
>   coax cables are needed to transfer the desired signal from one place
>   to another.  The result is the measurement system is not as  good as
>   it could be.
>   
Not if you use the built in mixer RF transformers to eliminate low 
frequency ground lops at the mixer input and use optical isolation for 
the output of the zero crossing detector comparator.
In other words a PCB using surface or through hole mount mixers is far 
better than using a packaged mixer with a common low frequency ground 
for all inputs and outputs.
It also pays to use a capacitive IF port termination for low beat 
frequencies (<100kHz) as this reduces the noise significantly.
>   There is a solution to this problem. Another kind of mixer  called a
>   "digital mixer"  is ideally suited for this application.  It  uses a
>   d-flop, with one signal going to the clock pin, and one going to the
>   "D" input.  The resulting signal on the "Q' output is  the frequency
>   difference between the two signals.
>   
And this isnt affected by low frequency ground loops?
>   The output signal is a full logic level swing, perhaps 5 Volts, with
>   a risetime  of a couple of nanoseconds. This is an  ideal  signal to
>   pass on  a terminated coax cable to the counter.  The  schematic and
>   waveforms are shown in the attached GIF.
>
>   The output  of  the  first d-flop is passed to  a  second  d-flop to
>   eliminate glitches due to metastability in the first stage. This can
>   occur when  the signal on the "D" input is exactly on  the switching
>   threshold when the clock transition occurs. The resulting glitch can
>   severely disrupt the following logic stages.
>
>   In practice, it might be difficult to offset two  stable oscillators
>   by 1  Hz.  In this case, the frequencies can be  multiplied  to some
>   higher value. For example, the frequencies could be multiplied  by a
>   factor of 10 to 100MHz, and offset by 1 Hz.
>
>   There may be some jitter in the leading edge of the beat  note since
>   the d-flop  may  or may not catch the transition as  it  crosses the
>   threshold on  the  "D" input. Instead of the  standard  +/-  1 clock
>   ambiguity in  digital circuits, the output could  be  several clocks
>   late. However,  if the counter had a resolution  of  100 nanoseconds
>   (10MHz clock),  the  extra  delay  is 

Re: [time-nuts] What is the best counter for a Time Nuts?

[Magnus Danielson]

Mike,

Mike Monett wrote:
>   The Allen deviation is used to describe the performance of  a stable
>   clock. Measuring the performance of a good clock requires  a counter
>   with resolution  down  to picosecond levels. As  Dr  Griffith points
>   out, some  modern counters may have internal signal  processing that
>   makes them unsuitable for this task.

Hold on!

What modern counters do is to use various means to improve on frequency 
and period measures. This makes the frequency and period measures 
unsuitable for futher processing as well as evaluation of expected 
performance when doing measures for Allan Deviation. However, what we do 
is usually not that measure, we to Time Interval measures for individual 
trigger points. When doing those measures these smoothing methods cannot 
be utilized. Then you are running on the bare-bone hardware performance 
with only the normal (traditional) translation skews.

I specifically cautioned Ulrich from making Allan Deviation performance 
estimate from the frequency performence for this reason. The smoothing 
will make such rule-of-thumb comparisions much harder.

>   Another thread  discussed using a mixer to  generate  the difference
>   frequency between  two oscillators, then measuring the  stability of
>   the resulting beat note:
> 
>   http://www.febo.com/pipermail/time-nuts/2005-July/019006.html
> 
>   The basic  principle  is sound. If the oscillators  were  running at
>   10MHz, and  the  frequency difference was 1 Hz, then  the  beat note
>   would be 1 Hz.
> 
>   This represents  one  part in 10 million, or  1e-7  of  the original
>   frequency. If  the  beat   note   is   measured  with  1 microsecond
>   resolution, the  overall resolution is 1e-7 / 1e-6 = 1e-13.  This is
>   beyond the capability of most commercial counters.
> 
>   The difficulty  with this approach is the output of a mixer is  at a
>   fairly low  level, perhaps 50 millivolts or so. The  frequency would
>   also be very low, perhaps 1 Hz. This means the counter would have to
>   trigger accurately on a very slow-rising, low amplitude signal.

This is not the actual problem. The actual problem is the slew rate of 
the signal. Even if the amplitude was several volts peak-to-peak the 
slew rate of the beat note is the main problem as the wideband noise of 
at the output added with the wideband noise of the counter input causes 
a random additive voltage modulation which can pre/post trigger around 
the ideal position with a RMS value of t_jitter = N_total / SR (this is 
a traditional trigger jitter formula).

The gain stages / slew rate amplifiers that Bruce and I have discussed 
contributes a significant gain which significantly goes beyond what a 
can come out of a mixer. Signal is clipped and filtered in order to 
improve signal to noise properties such that a minimal of noise is 
amplified while the slew rate is raised significantly.

>   This is  a very difficult measurement problem. The accuracy  will be
>   degraded by  noise,  such  as the 60Hz  AC  line  frequency  and its
>   harmonics, switching noise from the pc power supplies  and monitors,
>   radiation from nearby fluorescent lighting, plus thermal  noise from
>   the mixer and input stage of the amplifiers.

Not too hard really. The thing which makes it complex is that good 
signal to noise is needed both at the carrier frequency and beat 
frequency. Some knowledge of suitable measures should give adequate 
measures.

>   This low-level noise is very difficult to eliminate, especially when
>   coax cables are needed to transfer the desired signal from one place
>   to another.  The result is the measurement system is not as  good as
>   it could be.

Is it? Fighting ground loops to handle H fields is no big magic. Using 
mixers which ports is galvanically isolated helps. E fields is easier to 
handle at lower frequencies.

For the output port, the difference frequency needs the signal to noise 
properties. Traditional diffrential signal handling deals with both E 
and H field issues to such a level that other sources will dominate.

It should also be pointed out that carefull adjustment of both input 
port levels and the loading on the output port will have impact on 
performance as recorded in literature.

>   There is a solution to this problem. Another kind of mixer  called a
>   "digital mixer"  is ideally suited for this application.  It  uses a
>   d-flop, with one signal going to the clock pin, and one going to the
>   "D" input.  The resulting signal on the "Q' output is  the frequency
>   difference between the two signals.
> 
>   The output signal is a full logic level swing, perhaps 5 Volts, with
>   a risetime  of a couple of nanoseconds. This is an  ideal  signal to
>   pass on  a terminated coax cable to the counter.  The  schematic and
>   waveforms are shown in the attached GIF.

You will not solve the requirements for good dynamics. The digital input 
is highly non-linear and thus behaves like a m

Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Magnus Danielson wrote:
> Bruce,
>
>   
>> When measuring the frequency of a signal using a conventional counter,
>> increasing the gate time decreases the noise contribution of trigger
>> jitter to frequency measurement noise although jitter is invariant with
>> gate time. The jitter simply becomes a smaller fraction of the total
>> gate time. Similarly the frequency measurement resolution increases with
>> increasing gate time although the resolution (measured in picoseconds)
>> is invariant with gate time it simply becomes a smaller fraction of the
>> total gate time.
>> 
>
> True, I was being a bit sloppy there...
>
>   
>> However if one timestamps a few more signal zero crossings within the
>> gate time interval than just those and the start and end of the gate
>> time lower noise estimators of the frequency are available.
>> 
>
> Indeed.
>
>   
>> The HP53132 averages the frequency estimates for a series of identical
>> duration overlapped gate times.
>> Enrico's paper analyses this case.
>> The Australian paper corrects some of the errors in Enrico's analysis
>> and hints how the analysis may be extended to cover the case of counters
>> that use other resolution enhancement techniques.
>> 
>
> Recommended reading!
>
>   
>> Counters like the Pendulum CNT91 in effect time stamp every Nth zero
>> crossing of the signal and fit a linear regression line to the sequence
>> of time stamps. The frequency is then estimated from the slope of the
>> regression line. However the CNT91 has limited memory and processing
>> power so that full advantage isnt taken of the resolution offered by
>> this technique.
>> AFAIK no one has yet done a similar analysis to that done for the
>> "triangular" averaging counter (by Enrico and the Australians) for a
>> counter that does a regression line fit.
>> 
>
> Actually, as I recall it, there was a note in one of those articles
> relating to it, but your could figure out that it was rendering about the
> same conclusion. It also makes sense.
>
> Cheers,
> Magnus
>   
Hej Magnus

Of course such enhanced resolution techniques arent restricted purely to 
frequency measurement.
An analogous technique can be used in an integrating DVM where the 
integrator output is sampled periodically during the signal integration.
Even when a "multislope" technique is used during integrator runup, such 
a technique can be used.
In this case a form of sigma delta modulation is used to keep the 
integrator output within bounds and minimise the effect of dielectric 
absorption.
The accumulated quantised feedback is combined with the sampled 
integrator residue to form the equivalent of samples taken from an ideal 
integrator with a very large output range.
One can then use regression techniques to fit a straight line (or other 
curve) to the integrator output.
This will be most effective when the noise of the ADC used to sample the 
integrator residue is the dominant noise source and the input signal is 
relatively quiet with no significant spurious frequency components.

Bruce


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Re: [time-nuts] What is the best counter for a Time Nuts?

[Magnus Danielson]

Tom Duckworth wrote:
> Ulrich,
>
> Check out a Pendulum Instruments CNT-91 time stamping counter. You'll
find
> much better resolution. This counter doesn't work the way other
> direct/reciprocal counters do. It has 50 ps resolution time resolution
and
> 12 digits per second display.

The actual resolution is higher, but 50 ps is the published number.

Cheers,
Magnus





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Re: [time-nuts] What is the best counter for a Time Nuts?

[SAIDJACK]

Hi guys,
 
thanks for the hint, this explains it.
 
read the manual, and so it seems I cannot use time arming mode. How do you  
guys get around this? Do A to B measurements on the two channels?
 
thanks,
Said
 
 
In a message dated 10/9/2008 08:49:59 Pacific Daylight Time,  
[EMAIL PROTECTED] writes:

>>  Hi Tom, Ulrich,
>>
>> can't seem to get 12 digits/s out of  my 53132A in frequency mode when
>> doing
>> measurement  offset of -10MHz. I only get 11 digits/s for some reason.
>> Have  to
>> go  to 10s + gate time to get better  resolution.
>
> Correct. When you get "close" to an exact 10 MHz  input then
> the counter drops down into a "reduced resolution" mode  and
> you lose a digit (regardless of gate time). If you need, you  can
> query this with the :DIAG:MEAS:PRES? command. Details are
>  in the back of the 53132A manual.

"Additional Considerations for Digits  and Time Arming Modes" (at page 3-13
in my version of the  manual).

Cheers,
Magnus

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Magnus Danielson]

>> Hi Tom, Ulrich,
>>
>> can't seem to get 12 digits/s out of my 53132A in frequency mode when
>> doing
>> measurement offset of -10MHz. I only get 11 digits/s for some reason.
>> Have to
>> go  to 10s + gate time to get better resolution.
>
> Correct. When you get "close" to an exact 10 MHz input then
> the counter drops down into a "reduced resolution" mode and
> you lose a digit (regardless of gate time). If you need, you can
> query this with the :DIAG:MEAS:PRES? command. Details are
> in the back of the 53132A manual.

"Additional Considerations for Digits and Time Arming Modes" (at page 3-13
in my version of the manual).

Cheers,
Magnus

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Tom Van Baak]

> Hi Tom, Ulrich,
> 
> can't seem to get 12 digits/s out of my 53132A in frequency mode when doing  
> measurement offset of -10MHz. I only get 11 digits/s for some reason. Have to 
> go  to 10s + gate time to get better resolution.

Correct. When you get "close" to an exact 10 MHz input then
the counter drops down into a "reduced resolution" mode and
you lose a digit (regardless of gate time). If you need, you can
query this with the :DIAG:MEAS:PRES? command. Details are
in the back of the 53132A manual.

/tvb


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Re: [time-nuts] What is the best counter for a Time Nuts?

[Magnus Danielson]

Bruce,

> When measuring the frequency of a signal using a conventional counter,
> increasing the gate time decreases the noise contribution of trigger
> jitter to frequency measurement noise although jitter is invariant with
> gate time. The jitter simply becomes a smaller fraction of the total
> gate time. Similarly the frequency measurement resolution increases with
> increasing gate time although the resolution (measured in picoseconds)
> is invariant with gate time it simply becomes a smaller fraction of the
> total gate time.

True, I was being a bit sloppy there...

> However if one timestamps a few more signal zero crossings within the
> gate time interval than just those and the start and end of the gate
> time lower noise estimators of the frequency are available.

Indeed.

> The HP53132 averages the frequency estimates for a series of identical
> duration overlapped gate times.
> Enrico's paper analyses this case.
> The Australian paper corrects some of the errors in Enrico's analysis
> and hints how the analysis may be extended to cover the case of counters
> that use other resolution enhancement techniques.

Recommended reading!

> Counters like the Pendulum CNT91 in effect time stamp every Nth zero
> crossing of the signal and fit a linear regression line to the sequence
> of time stamps. The frequency is then estimated from the slope of the
> regression line. However the CNT91 has limited memory and processing
> power so that full advantage isnt taken of the resolution offered by
> this technique.
> AFAIK no one has yet done a similar analysis to that done for the
> "triangular" averaging counter (by Enrico and the Australians) for a
> counter that does a regression line fit.

Actually, as I recall it, there was a note in one of those articles
relating to it, but your could figure out that it was rendering about the
same conclusion. It also makes sense.

Cheers,
Magnus

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Magnus Danielson wrote:
> I think you mixed up the HP 53132A A-approximation with the Pendulum 
> linear regression. They are two distinct methods of improvements for the 
> intended application. Both have properties which does not make their 
> readings appropriate for Allan deviation calculations, as indicated in 
> the paper.
>
> Ulrich particular concern was the HP 53132A and then the triangular 
> approximation is the relevant one.
>
> One should recall that the properties of a system cannot be concluded in 
> a single parameter. Single-shot resolution is not everything, trigger 
> jitter, low frequency modulations, cross-talk, etc. etc. all come into 
> play to skew results before we can treat them by beutiful math.
>
> Single-shot resultion is an indication at best.
>
> Look at the HP 53132A where the single-shot resolution is 150 ps but the 
> trigger jitter is only 3 ps. Those numbers behave differently to gate 
> time and averaging. Increasing the gate time between a start and stop 
> trigger will increase the number virtual cycles you have, but the 
> trigger jitter for each start and stop will remain at 3 ps and thus 
> forming the floor which pure gate time cannot reduce. For this averaging 
> is needed.
>
> This is really what those ugly formulas in the back of the manual says. 
> Staffans papper above give some insight.
>
> Cheers,
> Magnus
>   
Magnus

When measuring the frequency of a signal using a conventional counter, 
increasing the gate time decreases the noise contribution of trigger 
jitter to frequency measurement noise although jitter is invariant with 
gate time. The jitter simply becomes a smaller fraction of the total 
gate time. Similarly the frequency measurement resolution increases with 
increasing gate time although the resolution (measured in picoseconds) 
is invariant with gate time it simply becomes a smaller fraction of the 
total gate time.

However if one timestamps a few more signal zero crossings within the 
gate time interval than just those and the start and end of the gate 
time lower noise estimators of the frequency are available.

The HP53132 averages the frequency estimates for a series of identical 
duration overlapped gate times.
Enrico's paper analyses this case.
The Australian paper corrects some of the errors in Enrico's analysis 
and hints how the analysis may be extended to cover the case of counters 
that use other resolution enhancement techniques.

Counters like the Pendulum CNT91 in effect time stamp every Nth zero 
crossing of the signal and fit a linear regression line to the sequence 
of time stamps. The frequency is then estimated from the slope of the 
regression line. However the CNT91 has limited memory and processing 
power so that full advantage isnt taken of the resolution offered by 
this technique.
AFAIK no one has yet done a similar analysis to that done for the 
"triangular" averaging counter (by Enrico and the Australians) for a 
counter that does a regression line fit.

Bruce

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Ulrich Bangert]

Gentlemen,

first of all I would like to thank you for your feedback. 

Reading in the literature that some of you supplied revealed that modern
counters may work even more tricky than i had though but that their
"tricky output" is NOT easily taken as the input for AD computations
without additional precautions.

> The Ref Output on the front panel of the SR620 is derived 
> (1/10,000) from the 
> EXT IN on the rear panel.  So when you apply a 10 MHz signal 
> to EXT IN you get 
> a 1 kHz REF OUT.  Appendix B in the PSR10 Rubidium source 
> manual describes how 
> to use this along with the arming function to average 1,000 
> measurements per 
> second resulting in 2E-12 per second on the display.  i.e. 
> very close to the 
> HP53132A.  So no external hardware is required and no PC to 
> get this result.

After I had read this suggestion of Brooke I immediately gave it a test.
With a reference and a DUT both believed (due to other
experiements/measurements) to be stable < 3E-12 @ 1s I received the
results attached.

And of course you do not get a frequency value as

> second resulting in 2E-12 per second on the display

may indicate. The counter works in time interval mode in this
arrangement and you get 1 s data of delta ts between 0 and 100 ns that
need to be un-wrapped. I would judge that this method is well suited if
a DUT needs to be trimmed to 10 NHz with high resolution but I fear that
it does not help us in high stability measurements since the intrinsic
noise is still more than a decade too high.

Best regards
Ulrich Bangert

> -Ursprungliche Nachricht-
> Von: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] Im Auftrag von Brooke Clarke
> Gesendet: Mittwoch, 8. Oktober 2008 23:43
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] What is the best counter for a Time Nuts?
> 
> 
> Hi Bruce:
> 
> The Ref Output on the front panel of the SR620 is derived 
> (1/10,000) from the 
> EXT IN on the rear panel.  So when you apply a 10 MHz signal 
> to EXT IN you get 
> a 1 kHz REF OUT.  Appendix B in the PSR10 Rubidium source 
> manual describes how 
> to use this along with the arming function to average 1,000 
> measurements per 
> second resulting in 2E-12 per second on the display.  i.e. 
> very close to the 
> HP53132A.  So no external hardware is required and no PC to 
> get this result.
> 
> Have Fun,
> 
> Brooke Clarke
> http://www.prc68.com
> http://www.precisionclock.com
> 
> 
> Bruce Griffiths wrote:
> .
> > 
> > It is also possible to use a SR620 or a 5370 to take 1000 
> > timestamps/sec. However may require using some external hardware 
> > (frequency divider). For maximum accuracy and precision the 
> resultant 
> > data has to be logged and processed off line using a PC or other 
> > computer.
> > 
> 
> 
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> 


SR620.pdf
Description: Adobe PDF document
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Re: [time-nuts] What is the best counter for a Time Nuts?

[Magnus Danielson]

Bruce Griffiths wrote:
> Ulrich Bangert wrote:
>> Gentlemen,
>>
>> up to now I have been thinking that I am pretty well informed about
>> current counter technology but some experiences of the last days make me
>> doubt. The following applies to frequency measurements of a 10 MHz
>> signal.
>>
>> I have received some data measured with an Agilent 53131 counter from
>> Time Nuts member James Miller. That data shows a resolution of 3 digits
>> after the decimal point for a frequency measurement of 1 s "Gate time"
>> and 4 digits for a 10 s "Gate time". 
>>
>> This is perfectly in line with what I thought to know about modern
>> counters: Internally EVERY type of measurement is reduced to a time
>> interval measurement. Since a frequency measurement with 1 s "Gate time"
>> equals a time interval measurement of an 1 s interval and the counter
>> has an single shot resolution of 500 ps the relative statistical error
>> due to this resolution is 500 ps / 1 s = 5*E-10. As the frequency is
>> computed from the time interval measurement is has the same relative
>> error and for that reason displaying 3 digits after the decimal point is
>> a good choice because 0.001 Hz (1E-10) is the least digit of
>> significance. Using a digit more would suggest a resolution that is not
>> available, using one digit less would decrease the numerical resolution
>> below the measurement resolution. 
>>
>> Up to this point my statement of beliefs is in harmony with Agilent.
>>
>> Now comes the strange part: In the course of a discussion between Time
>> Nuts member Bernd Neubig of AXTAL Germany and me I received data
>> measured with an Agilent 53132 which is the 53131's big brother with a
>> better single shot resolution of 150 ps. 
>>
>> I have been prepared to see this better resolution in the data but what
>> I really have seen SHOCKED me a lot. Not only does the 53132 generate 5
>> (!) digits after the decimal point for a 1 s "Gate time" (with 0.1
>> equal to 1E-12) a sigma tau diagram of the data revealed that the last
>> digit was not only "noise" but seemed to be of real significance. I had
>> been presuming that perhaps the counter's statistics had been enabled
>> for that but as it turned out this was not the case. From that data one
>> must make the conclusion that the overall jitter of the 53132 including
>> the resolution quantification, trigger errors and everything else is
>> <=5E-12 !!
>>
>> Big question: If the single shot resolution is only 3-4 times better
>> that that of the 53131 and much inferior to the 20 ps of my SR620, how
>> does the 53132 manage to be THAT GOOD A PERFORMER? Magic? Black art? 
>>
>> I immediatly made the same measurement with my SR620 to receive a
>> counter noise floor of 6E-11 for 1 s frequency data, pretty much a
>> decade worse of the 53132. Must we throw our 5370s and SR620s out of the
>> window and settle for second hand  53132 from eBay to make precise
>> stability measurements ???
>>
>> TIA for your suggestions
>>
>> Ulrich Bangert
>> www.ulrich-bangert.de
>> Ortholzer Weg 1
>> 27243 Gross Ippener 
>>
>>
>>   
> Ulrich
> 
> These effectively counters time stamp every Nth signal zero crossing and 
> then fit a linear regression line to the results.
> This reduces the effective noise contribution from the interpolator.
> Since the noise transfer function is thereby altered over that of a 
> conventional counter or reciprocal counter one cannot use the results to 
> compute the Allen deviation directly.
> 
> Read the papers on the Pendulum site for further details.
> 
> http://www.pendulum-instruments.com/Assets/download/frequency_counting_article.pdf
> 
> http://www.pendulum-instruments.com/Assets/download/timestamping_article.pdf
> 
> Enrico Rubiola published a paper on the effect of using the output from 
> such counters in that Allen deviation calculations.
> 
> http://arxiv.org/abs/physics?papernum=0411227
> 
> A recent Australian paper purports to correct some of the errors in 
> Enrico's paper, but the basic conclusion is the same one cannot 
> calculate the Allen deviation directly from measurements obtained with 
> such a counter.

I think you mixed up the HP 53132A A-approximation with the Pendulum 
linear regression. They are two distinct methods of improvements for the 
intended application. Both have properties which does not make their 
readings appropriate for Allan deviation calculations, as indicated in 
the paper.

Ulrich particular concern was the HP 53132A and then the triangular 
approximation is the relevant one.

One should recall that the properties of a system cannot be concluded in 
a single parameter. Single-shot resolution is not everything, trigger 
jitter, low frequency modulations, cross-talk, etc. etc. all come into 
play to skew results before we can treat them by beutiful math.

Single-shot resultion is an indication at best.

Look at the HP 53132A where the single-shot resolution is 150 ps but the 
trigger jitter is only 3 ps. Those numbers

Re: [time-nuts] What is the best counter for a Time Nuts?

[SAIDJACK]

Hi Tom, Ulrich,
 
can't seem to get 12 digits/s out of my 53132A in frequency mode when doing  
measurement offset of -10MHz. I only get 11 digits/s for some reason. Have to 
go  to 10s + gate time to get better resolution.
 
But I think I discussed this before on this forum, the highest resolution  
time interval counter available at hobby price points on Ebay is the  Wavecrest 
DTS series, and several members of this forum use these quite  successfully. 
They have a nice Windows based user interface via GPIB, or  front-panel 
operation.
 
DTS-2075 for example has 0.8ps(!) hardware resolution, 10ps typical  noise 
rms (I see more like <3ps rms noise on my units), and +/-30ps single  shot 
accuracy. They are self-calibrating using front panel buttons and some SMA  
cables.
 
Lastly they can do cable-length measurements to below 1ps resolution!
 
That combined with 40K samples/s gives a lot of bang (for the buck).
 
You can measure period jitter against the internal oven with a typ. noise  
floor of 3ps, or frequency stability against an external reference. Low end  
units will measure DC to above 1GHz.
 
I have bought working units on Ebay for less than $500 in the past. But  they 
won't please everyone, they are clunky/noisy, and consume a lot of  power.
 
bye,
Said
 
 
In a message dated 10/9/2008 00:30:04 Pacific Daylight Time,  
[EMAIL PROTECTED] writes:

Ulrich,

Check out a Pendulum Instruments CNT-91 time stamping  counter. You'll find
much better resolution. This counter doesn't work the  way other
direct/reciprocal counters do. It has 50 ps resolution time  resolution and
12 digits per second display.

Tom
Tom  Duckworth
510-886-1396




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Re: [time-nuts] What is the best counter for a Time Nuts?

[Tom Duckworth]

Ulrich,

Check out a Pendulum Instruments CNT-91 time stamping counter. You'll find
much better resolution. This counter doesn't work the way other
direct/reciprocal counters do. It has 50 ps resolution time resolution and
12 digits per second display.

Tom
Tom Duckworth
510-886-1396
 
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Bruce Griffiths
Sent: Wednesday, October 08, 2008 1:34 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] What is the best counter for a Time Nuts?

Ulrich Bangert wrote:
> Gentlemen,
>
> up to now I have been thinking that I am pretty well informed about
> current counter technology but some experiences of the last days make me
> doubt. The following applies to frequency measurements of a 10 MHz
> signal.
>
> I have received some data measured with an Agilent 53131 counter from
> Time Nuts member James Miller. That data shows a resolution of 3 digits
> after the decimal point for a frequency measurement of 1 s "Gate time"
> and 4 digits for a 10 s "Gate time". 
>
> This is perfectly in line with what I thought to know about modern
> counters: Internally EVERY type of measurement is reduced to a time
> interval measurement. Since a frequency measurement with 1 s "Gate time"
> equals a time interval measurement of an 1 s interval and the counter
> has an single shot resolution of 500 ps the relative statistical error
> due to this resolution is 500 ps / 1 s = 5*E-10. As the frequency is
> computed from the time interval measurement is has the same relative
> error and for that reason displaying 3 digits after the decimal point is
> a good choice because 0.001 Hz (1E-10) is the least digit of
> significance. Using a digit more would suggest a resolution that is not
> available, using one digit less would decrease the numerical resolution
> below the measurement resolution. 
>
> Up to this point my statement of beliefs is in harmony with Agilent.
>
> Now comes the strange part: In the course of a discussion between Time
> Nuts member Bernd Neubig of AXTAL Germany and me I received data
> measured with an Agilent 53132 which is the 53131's big brother with a
> better single shot resolution of 150 ps. 
>
> I have been prepared to see this better resolution in the data but what
> I really have seen SHOCKED me a lot. Not only does the 53132 generate 5
> (!) digits after the decimal point for a 1 s "Gate time" (with 0.1
> equal to 1E-12) a sigma tau diagram of the data revealed that the last
> digit was not only "noise" but seemed to be of real significance. I had
> been presuming that perhaps the counter's statistics had been enabled
> for that but as it turned out this was not the case. From that data one
> must make the conclusion that the overall jitter of the 53132 including
> the resolution quantification, trigger errors and everything else is
> <=5E-12 !!
>
> Big question: If the single shot resolution is only 3-4 times better
> that that of the 53131 and much inferior to the 20 ps of my SR620, how
> does the 53132 manage to be THAT GOOD A PERFORMER? Magic? Black art? 
>
> I immediatly made the same measurement with my SR620 to receive a
> counter noise floor of 6E-11 for 1 s frequency data, pretty much a
> decade worse of the 53132. Must we throw our 5370s and SR620s out of the
> window and settle for second hand  53132 from eBay to make precise
> stability measurements ???
>
> TIA for your suggestions
>
> Ulrich Bangert
> www.ulrich-bangert.de
> Ortholzer Weg 1
> 27243 Gross Ippener 
>
>
>   
Ulrich

These effectively counters time stamp every Nth signal zero crossing and 
then fit a linear regression line to the results.
This reduces the effective noise contribution from the interpolator.
Since the noise transfer function is thereby altered over that of a 
conventional counter or reciprocal counter one cannot use the results to 
compute the Allen deviation directly.

Read the papers on the Pendulum site for further details.

http://www.pendulum-instruments.com/Assets/download/frequency_counting_artic
le.pdf

http://www.pendulum-instruments.com/Assets/download/timestamping_article.pdf

Enrico Rubiola published a paper on the effect of using the output from 
such counters in that Allen deviation calculations.

http://arxiv.org/abs/physics?papernum=0411227

A recent Australian paper purports to correct some of the errors in 
Enrico's paper, but the basic conclusion is the same one cannot 
calculate the Allen deviation directly from measurements obtained with 
such a counter.


Bruce

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Bruce Griffiths wrote:
> Brooke Clarke wrote:
>   
>> Hi Bruce:
>>
>> The Ref Output on the front panel of the SR620 is derived (1/10,000) from 
>> the 
>> EXT IN on the rear panel.  So when you apply a 10 MHz signal to EXT IN you 
>> get 
>> a 1 kHz REF OUT.  Appendix B in the PSR10 Rubidium source manual describes 
>> how 
>> to use this along with the arming function to average 1,000 measurements per 
>> second resulting in 2E-12 per second on the display.  i.e. very close to the 
>> HP53132A.  So no external hardware is required and no PC to get this result.
>>
>> Have Fun,
>>   
>> 
> Brooke
>
> Now I am back on my own network, Here's is what I actually intended to post.
>
> That only works well when averaging a fixed time interval or phase error.
> In general with a frequency input, the unwrapped phase measures are 
> linear in time.
> You need to process the raw measurements to unwrap the phase and fit a 
> linear regression line to the unwrapped phase.
> You also need to divide down the frequency to produce an output 
> frequency that is less than the maximum measurement transfer rate  to 
> the PC.
> If I remember correctly the 5370 (in binary mode) can transfer more 
> measurements per second than the SR620.
>
> So in this case the older hardware has a speed advantage although it 
> needs a pair of external frequency dividers (the extra one is used to 
> divide down your frequency reference to a convenient frequency for the 
> STOP input greater than the divided down input frequency connected to 
> the START input.).
>
> Grenhall's picket fence algorithm can then be used to unwrap the 
> measured time intervals into the corresponding time stamps.
>
> Bruce
>
>   
Addendum:

It also can be made to work well for the case where there is only an 
occasional single phase wrap per averaging period.
This applies to the case when the 2 frequencies being compared are 
within 1Hz or so of one another as in the case discussed in the PRS10 
manual appendix.
When there are many phase wraps per averaging time it becomes 
difficult/impossible to reliably account for such phase wraps without 
access to the raw measurements.

Bruce

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Brooke Clarke wrote:
> Hi Bruce:
>
> The Ref Output on the front panel of the SR620 is derived (1/10,000) from the 
> EXT IN on the rear panel.  So when you apply a 10 MHz signal to EXT IN you 
> get 
> a 1 kHz REF OUT.  Appendix B in the PSR10 Rubidium source manual describes 
> how 
> to use this along with the arming function to average 1,000 measurements per 
> second resulting in 2E-12 per second on the display.  i.e. very close to the 
> HP53132A.  So no external hardware is required and no PC to get this result.
>
> Have Fun,
>   
Brooke

Now I am back on my own network, Here's is what I actually intended to post.

That only works well when averaging a fixed time interval or phase error.
In general with a frequency input, the unwrapped phase measures are 
linear in time.
You need to process the raw measurements to unwrap the phase and fit a 
linear regression line to the unwrapped phase.
You also need to divide down the frequency to produce an output 
frequency that is less than the maximum measurement transfer rate  to 
the PC.
If I remember correctly the 5370 (in binary mode) can transfer more 
measurements per second than the SR620.

So in this case the older hardware has a speed advantage although it 
needs a pair of external frequency dividers (the extra one is used to 
divide down your frequency reference to a convenient frequency for the 
STOP input greater than the divided down input frequency connected to 
the START input.).

Grenhall's picket fence algorithm can then be used to unwrap the 
measured time intervals into the corresponding time stamps.

Bruce

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Brooke Clarke]

Hi Bruce:

The Ref Output on the front panel of the SR620 is derived (1/10,000) from the 
EXT IN on the rear panel.  So when you apply a 10 MHz signal to EXT IN you get 
a 1 kHz REF OUT.  Appendix B in the PSR10 Rubidium source manual describes how 
to use this along with the arming function to average 1,000 measurements per 
second resulting in 2E-12 per second on the display.  i.e. very close to the 
HP53132A.  So no external hardware is required and no PC to get this result.

Have Fun,

Brooke Clarke
http://www.prc68.com
http://www.precisionclock.com


Bruce Griffiths wrote:
.
> 
> It is also possible to use a SR620 or a 5370 to take 1000 timestamps/sec.
> However may require using some external hardware (frequency divider).
> For maximum accuracy and precision the resultant data has to be logged 
> and processed off line using a PC or other computer.
> 


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Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Tom Van Baak wrote:
> Hi Ulrich,
>
> My understanding is that 1) the 53132A has a single-shot
> resolution of about 150 ps, but also 2) it can do something like
> 200,000 phase measurement per second for CW RF inputs.
>
> In frequency mode, the frequency computed and displayed
> each second is the result of internal statistics on those
> 200,000 samples, which in general is much better than two
> single TI measurements made 1 second apart.
>
> In the best case of no correlation between input and timebase
> the frequency resolution would be 150 ps / sqrt(200 000), which
> is sub-ps.
>
> In reality, depending on the numerical character of the input RF
> frequency, you don't get the full sqrt(20) factor. Page 3-13
> of the 53132A user manual tries to explain this. But for most
> input frequencies it is in the low picoseconds, which is why it
> can be called a 12-digit per second counter. Google for
> 53132a user manual for a copy of the manual.
>
>   
It is feasible to achieve a somewhat higher timestamp resolution (~20ps) 
and continuous sampling rate (> 1.5MSPS) than those of the 53132A 
relatively inexpensively provided that a DSP or similar processor is 
used to process the time stamp  data in real time.

It is also possible to use a SR620 or a 5370 to take 1000 timestamps/sec.
However may require using some external hardware (frequency divider).
For maximum accuracy and precision the resultant data has to be logged 
and processed off line using a PC or other computer.

> (As an aside, if you use a 53132A on a slowly warming OCXO
> you can see the display resolution change when the magic n/m
> threshold, mentioned in the back of the manual, is crossed).
>
> The bottom line is that the SR 620 or hp 5370 is a better counter
> for TI (single-shot) measurements (e.g., comparing 1 PPS ticks).
> But for CW frequency measurements, the 53132A is much quicker
> due to this extreme internal oversampling. To be fair, I'm pretty
> sure that other modern counters (e.g., Philips, Pendulum) also
> use this frequency resolution trick.
>
> /tvb
>   
Some Pendulum (A Philips spinoff) and Fluke (rebadged Pendulum) counters 
do use an improved (fit linear regression line to time sequence) 
statistical technique.

Bruce

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Tom Van Baak wrote:
>> Big question: If the single shot resolution is only 3-4 times better
>> that that of the 53131 and much inferior to the 20 ps of my SR620, how
>> does the 53132 manage to be THAT GOOD A PERFORMER? Magic? Black art? 
>> 
>
> Hi Ulrich,
>
> My understanding is that 1) the 53132A has a single-shot
> resolution of about 150 ps, but also 2) it can do something like
> 200,000 phase measurement per second for CW RF inputs.
>
> In frequency mode, the frequency computed and displayed
> each second is the result of internal statistics on those
> 200,000 samples, which in general is much better than two
> single TI measurements made 1 second apart.
>
> In the best case of no correlation between input and timebase
> the frequency resolution would be 150 ps / sqrt(200 000), which
> is sub-ps.
>
> In reality, depending on the numerical character of the input RF
> frequency, you don't get the full sqrt(20) factor. Page 3-13
> of the 53132A user manual tries to explain this. But for most
> input frequencies it is in the low picoseconds, which is why it
> can be called a 12-digit per second counter. Google for
> 53132a user manual for a copy of the manual.
>
> (As an aside, if you use a 53132A on a slowly warming OCXO
> you can see the display resolution change when the magic n/m
> threshold, mentioned in the back of the manual, is crossed).
>
> The bottom line is that the SR 620 or hp 5370 is a better counter
> for TI (single-shot) measurements (e.g., comparing 1 PPS ticks).
> But for CW frequency measurements, the 53132A is much quicker
> due to this extreme internal oversampling. To be fair, I'm pretty
> sure that other modern counters (e.g., Philips, Pendulum) also
> use this frequency resolution trick.
>
> /tvb
>
>   
The Australian IEEE paper details are:

/Considerations on the Measurement of the Stability of Oscillators with 
Frequency Counters, /Samuel T. Dawkins, John J. McFerran, Andre N Luiten.

All authors are from the School of Physics, university of Western Australia.

Bruce

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Tom Van Baak]

> Big question: If the single shot resolution is only 3-4 times better
> that that of the 53131 and much inferior to the 20 ps of my SR620, how
> does the 53132 manage to be THAT GOOD A PERFORMER? Magic? Black art? 

Hi Ulrich,

My understanding is that 1) the 53132A has a single-shot
resolution of about 150 ps, but also 2) it can do something like
200,000 phase measurement per second for CW RF inputs.

In frequency mode, the frequency computed and displayed
each second is the result of internal statistics on those
200,000 samples, which in general is much better than two
single TI measurements made 1 second apart.

In the best case of no correlation between input and timebase
the frequency resolution would be 150 ps / sqrt(200 000), which
is sub-ps.

In reality, depending on the numerical character of the input RF
frequency, you don't get the full sqrt(20) factor. Page 3-13
of the 53132A user manual tries to explain this. But for most
input frequencies it is in the low picoseconds, which is why it
can be called a 12-digit per second counter. Google for
53132a user manual for a copy of the manual.

(As an aside, if you use a 53132A on a slowly warming OCXO
you can see the display resolution change when the magic n/m
threshold, mentioned in the back of the manual, is crossed).

The bottom line is that the SR 620 or hp 5370 is a better counter
for TI (single-shot) measurements (e.g., comparing 1 PPS ticks).
But for CW frequency measurements, the 53132A is much quicker
due to this extreme internal oversampling. To be fair, I'm pretty
sure that other modern counters (e.g., Philips, Pendulum) also
use this frequency resolution trick.

/tvb



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Re: [time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Ulrich Bangert wrote:
> Gentlemen,
>
> up to now I have been thinking that I am pretty well informed about
> current counter technology but some experiences of the last days make me
> doubt. The following applies to frequency measurements of a 10 MHz
> signal.
>
> I have received some data measured with an Agilent 53131 counter from
> Time Nuts member James Miller. That data shows a resolution of 3 digits
> after the decimal point for a frequency measurement of 1 s "Gate time"
> and 4 digits for a 10 s "Gate time". 
>
> This is perfectly in line with what I thought to know about modern
> counters: Internally EVERY type of measurement is reduced to a time
> interval measurement. Since a frequency measurement with 1 s "Gate time"
> equals a time interval measurement of an 1 s interval and the counter
> has an single shot resolution of 500 ps the relative statistical error
> due to this resolution is 500 ps / 1 s = 5*E-10. As the frequency is
> computed from the time interval measurement is has the same relative
> error and for that reason displaying 3 digits after the decimal point is
> a good choice because 0.001 Hz (1E-10) is the least digit of
> significance. Using a digit more would suggest a resolution that is not
> available, using one digit less would decrease the numerical resolution
> below the measurement resolution. 
>
> Up to this point my statement of beliefs is in harmony with Agilent.
>
> Now comes the strange part: In the course of a discussion between Time
> Nuts member Bernd Neubig of AXTAL Germany and me I received data
> measured with an Agilent 53132 which is the 53131's big brother with a
> better single shot resolution of 150 ps. 
>
> I have been prepared to see this better resolution in the data but what
> I really have seen SHOCKED me a lot. Not only does the 53132 generate 5
> (!) digits after the decimal point for a 1 s "Gate time" (with 0.1
> equal to 1E-12) a sigma tau diagram of the data revealed that the last
> digit was not only "noise" but seemed to be of real significance. I had
> been presuming that perhaps the counter's statistics had been enabled
> for that but as it turned out this was not the case. From that data one
> must make the conclusion that the overall jitter of the 53132 including
> the resolution quantification, trigger errors and everything else is
> <=5E-12 !!
>
> Big question: If the single shot resolution is only 3-4 times better
> that that of the 53131 and much inferior to the 20 ps of my SR620, how
> does the 53132 manage to be THAT GOOD A PERFORMER? Magic? Black art? 
>
> I immediatly made the same measurement with my SR620 to receive a
> counter noise floor of 6E-11 for 1 s frequency data, pretty much a
> decade worse of the 53132. Must we throw our 5370s and SR620s out of the
> window and settle for second hand  53132 from eBay to make precise
> stability measurements ???
>
> TIA for your suggestions
>
> Ulrich Bangert
> www.ulrich-bangert.de
> Ortholzer Weg 1
> 27243 Gross Ippener 
>
>
>   
Ulrich

These effectively counters time stamp every Nth signal zero crossing and 
then fit a linear regression line to the results.
This reduces the effective noise contribution from the interpolator.
Since the noise transfer function is thereby altered over that of a 
conventional counter or reciprocal counter one cannot use the results to 
compute the Allen deviation directly.

Read the papers on the Pendulum site for further details.

http://www.pendulum-instruments.com/Assets/download/frequency_counting_article.pdf

http://www.pendulum-instruments.com/Assets/download/timestamping_article.pdf

Enrico Rubiola published a paper on the effect of using the output from 
such counters in that Allen deviation calculations.

http://arxiv.org/abs/physics?papernum=0411227

A recent Australian paper purports to correct some of the errors in 
Enrico's paper, but the basic conclusion is the same one cannot 
calculate the Allen deviation directly from measurements obtained with 
such a counter.


Bruce

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Re: [time-nuts] What is the best counter for a Time Nuts?

[Magnus Danielson]

Ulrich,

> up to now I have been thinking that I am pretty well informed about
> current counter technology but some experiences of the last days make me
> doubt. The following applies to frequency measurements of a 10 MHz
> signal.
>
> I have received some data measured with an Agilent 53131 counter from
> Time Nuts member James Miller. That data shows a resolution of 3 digits
> after the decimal point for a frequency measurement of 1 s "Gate time"
> and 4 digits for a 10 s "Gate time".
>
> This is perfectly in line with what I thought to know about modern
> counters: Internally EVERY type of measurement is reduced to a time
> interval measurement.

To a reciprocal counter base measurement. For an insight in what
calculations is performed to shape results, see the HP 5372A programmers
manual which discloses a lot of details.

> Since a frequency measurement with 1 s "Gate time"
> equals a time interval measurement of an 1 s interval and the counter
> has an single shot resolution of 500 ps the relative statistical error
> due to this resolution is 500 ps / 1 s = 5*E-10.

Actually you need to multiply by two since both the start and stop channel
has independent errors. If you look in the 53131A/132A manual you see

RMS resolution = sqrt(t_RES^2 + Start Trigger Error^2 + Stop Trigger Error^2)

 53131A  53132A
Trigger Error500 ps  150 ps
t_RES750 ps  300 ps

There is further details in the operational manual (chapter 3: Measurement
Specification).

> As the frequency is
> computed from the time interval measurement is has the same relative
> error and for that reason displaying 3 digits after the decimal point is
> a good choice because 0.001 Hz (1E-10) is the least digit of
> significance. Using a digit more would suggest a resolution that is not
> available, using one digit less would decrease the numerical resolution
> below the measurement resolution.
>
> Up to this point my statement of beliefs is in harmony with Agilent.

Certainly, and it matches the graphs in their manual very well.

> Now comes the strange part: In the course of a discussion between Time
> Nuts member Bernd Neubig of AXTAL Germany and me I received data
> measured with an Agilent 53132 which is the 53131's big brother with a
> better single shot resolution of 150 ps.
>
> I have been prepared to see this better resolution in the data but what
> I really have seen SHOCKED me a lot. Not only does the 53132 generate 5
> (!) digits after the decimal point for a 1 s "Gate time" (with 0.1
> equal to 1E-12) a sigma tau diagram of the data revealed that the last
> digit was not only "noise" but seemed to be of real significance. I had
> been presuming that perhaps the counter's statistics had been enabled
> for that but as it turned out this was not the case. From that data one
> must make the conclusion that the overall jitter of the 53132 including
> the resolution quantification, trigger errors and everything else is
> <=5E-12 !!
>
> Big question: If the single shot resolution is only 3-4 times better
> that that of the 53131 and much inferior to the 20 ps of my SR620, how
> does the 53132 manage to be THAT GOOD A PERFORMER? Magic? Black art?
>
> I immediatly made the same measurement with my SR620 to receive a
> counter noise floor of 6E-11 for 1 s frequency data, pretty much a
> decade worse of the 53132. Must we throw our 5370s and SR620s out of the
> window and settle for second hand  53132 from eBay to make precise
> stability measurements ???

No. I think you are seeing the result of the 53132A gliding window
averager. There are articles that details this estimator and basically
cuts it into small pieces for use in Allan deviation measures.

You are right in not believing your eyes.

I have a 53132A at work and a SR-620 at home. I could compare them to
verify your measurements. 10 MHz sources are plentiful.

What you really should do is to take a number of raw TI difference
measures and calculate the Allan deviation plots for both counters. I
think you will find that they will match the 500 ps and 150 ps curves will
match better.

Notice that the timing jitter changes from 50 ps to 3 ps between the models.

I can dig up more details as I get home if you don't get enought here and
from fellow time-nuts.

The short story is: Do NOT estimate expected Allan deviation noisefloors
from the (display) readings of your counter. There exist several
"resolution improvement" algorithms. These are to our benefit when using
the counter as a frequency or period estimator as we can get result
quicker, but these improvements does not ripple over to the Allan
deviation plots.

Cheers,
Magnus

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[time-nuts] What is the best counter for a Time Nuts?

[Ulrich Bangert]

Gentlemen,

up to now I have been thinking that I am pretty well informed about
current counter technology but some experiences of the last days make me
doubt. The following applies to frequency measurements of a 10 MHz
signal.

I have received some data measured with an Agilent 53131 counter from
Time Nuts member James Miller. That data shows a resolution of 3 digits
after the decimal point for a frequency measurement of 1 s "Gate time"
and 4 digits for a 10 s "Gate time". 

This is perfectly in line with what I thought to know about modern
counters: Internally EVERY type of measurement is reduced to a time
interval measurement. Since a frequency measurement with 1 s "Gate time"
equals a time interval measurement of an 1 s interval and the counter
has an single shot resolution of 500 ps the relative statistical error
due to this resolution is 500 ps / 1 s = 5*E-10. As the frequency is
computed from the time interval measurement is has the same relative
error and for that reason displaying 3 digits after the decimal point is
a good choice because 0.001 Hz (1E-10) is the least digit of
significance. Using a digit more would suggest a resolution that is not
available, using one digit less would decrease the numerical resolution
below the measurement resolution. 

Up to this point my statement of beliefs is in harmony with Agilent.

Now comes the strange part: In the course of a discussion between Time
Nuts member Bernd Neubig of AXTAL Germany and me I received data
measured with an Agilent 53132 which is the 53131's big brother with a
better single shot resolution of 150 ps. 

I have been prepared to see this better resolution in the data but what
I really have seen SHOCKED me a lot. Not only does the 53132 generate 5
(!) digits after the decimal point for a 1 s "Gate time" (with 0.1
equal to 1E-12) a sigma tau diagram of the data revealed that the last
digit was not only "noise" but seemed to be of real significance. I had
been presuming that perhaps the counter's statistics had been enabled
for that but as it turned out this was not the case. From that data one
must make the conclusion that the overall jitter of the 53132 including
the resolution quantification, trigger errors and everything else is
<=5E-12 !!

Big question: If the single shot resolution is only 3-4 times better
that that of the 53131 and much inferior to the 20 ps of my SR620, how
does the 53132 manage to be THAT GOOD A PERFORMER? Magic? Black art? 

I immediatly made the same measurement with my SR620 to receive a
counter noise floor of 6E-11 for 1 s frequency data, pretty much a
decade worse of the 53132. Must we throw our 5370s and SR620s out of the
window and settle for second hand  53132 from eBay to make precise
stability measurements ???

TIA for your suggestions

Ulrich Bangert
www.ulrich-bangert.de
Ortholzer Weg 1
27243 Gross Ippener 


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