[time-nuts] Dual Mixer

EWKehren at aol.com EWKehren at aol.com
Tue May 11 23:30:44 UTC 2010

Allow me to apologize to start this again. Bert
In a message dated 5/11/2010 7:25:39 P.M. Eastern Daylight Time,  
warrensjmail-one at yahoo.com writes:

(My  apologies to all, this is a game Bruce and I play every time I bring 
my  simple tester.)

Bruce wrote:
>"So you now actually  integrate/average the frequency over the sampling
>interval (Tau) after  rejecting the need to do this for months?"

Yes, I integrate/average  just the same as I have always done it from day 
Did you finally  understand how the integration works using most any ADC?
Hint: it's done  with oversampling the tau zero time.
(and a LP filter set to a value above  the tau zero but below the 
The VERY SAME thing I have  been trying to tell you from day one, something 
that you have chosen to  ignore.
The very original Block diagram that I posted shows it, if you need  more 



So  you now actually integrate/average the frequency over the sampling
interval  (Tau) after rejecting the need to do this for  months?


WarrenS wrote:
>  Bruce
> Before we go around again and discuses what my simple  tester can and
> can not do and why,
> It would be helpful if you  would take the time to better understand
> how it works and why it works  the way I have done it.
> You really should try one yourself if you  can't see why it works.
> You are going to be surprised and embarrassed  at how good it works.
> Why you're at it, try the "swing test" with  anything you have. Let me
> know how that goes.
> I'm not  saying that may tester will match someone's Latest ever
> changing NEW  idea of what the "correct AVAR" should be,
> After all it just Logs  correct, integrated, Freq difference data of
> ANY noise type
>  and does it without adding any dead time or aliasing all by using
>  pretty much using ANY ADC capability of over sampling at the tau Zero
>  rate.
> If one then uses the data log with something like the classic  Stable
> 32 S/W or Ulrich's Plotter,
> it gives is the exact same  results as other methods costing much much
> more, over the whole tau  range.
> This is limited only be its reference oscillator (Same way that  all
> others are limited of course, Doesn't get much better than  that).
> If that is not good enough for you, them you need to discuss  the
> results with Symmetricon and others that give the same answer as  mine,
> not me.
> If for some reason you want to set one  up wrong so that it matches the
> results of some other special  instrument, I'd be glad to tell you how
> to have it add back in the  dead time or aliasing artifact problems or
> whatever else you would  like it to do wrong, that it presently does
> correctly.
>  ws
> ******************
> Bruce wrote
> As  long as one is aware that your method (as implemented by you) doesn't
>  actually measure Allan variance, it may be useful for comparing the
>  relative stability some sources for small Tau (unfortunately the range
>  of Tau for which the method may produce useful results depends on the
>  phase noise characteristics of the sources being compared).
> To measure  AVAR the technique has to have the same response to all phase
> noise  spectral components as does AVAR.
> Since you do not integrate/average  the frequency measures the phase
> noise response of the method is not  identical to that used in
> calculating AVAR.
> This technique  probably works best when white phase noise dominates the
> phase noise  spectral region of interest (usually for small Tau).
> For those  who can follow the theory, the following paper shows how the
> above  method is affected by aliasing etc:
>  http://hal.archives-ouvertes.fr/docs/00/37/63/05/PDF/alaa_p1_v4a.pdf
>  The paper also shows how the required integration (needed to actually
>  measure AVAR) can be approximated from the discrete sample sequence.
>  Alternatively one could avoid the numerical integration by replacing  the
> ADC with a zero deadtime (ie not a dual slope converter. A  multislope
> algorithm like that used in the 34401A (but not the 3458A)  should work
> as the signal is integrated continuously) integrating ADC.  One
> possibility is to use a VFC as NIST did when they used this  technique
> some decades ago.
> Of course, the classical  DMTD setup undersamples the phase noise
> spectrum and thus may suffer  from aliasing artifacts.
> Such aliasing artifacts have no significant  effect when the phase noise
> spectrum is flat.
>  Bruce
> *********************
> WarrenS wrote:
>>  For the Really cheap time nuts,
>> It sounds like Bert  Kehren has done a great Job building a Dual Mixer
>>  tester.
>> There are other simpler, less standard ways to get good  data for Allan
>> Variance and small frequency  differences.
>> My VERY simple $10.00 analog tight PLL Tester BB  (Previously posted)
>> pretty much accomplishes the same goals as  his,
>> and it can do 1e-13 in a second, and 1e-11 in 10ms   (limited of course
>> by the single reference Oscillator  used)
>> A simple test that most can do at home, and  still challenges the best
>> high end testers out there is Tom's the  swinging Oscillator test.
>>  http://www.leapsecond.com/pages/10811-g/
>> (The results from my PLL  tester is attached)
>> ws
>>  ******************
>> ----- Original Message ----- From: <EWKehren  at aol.com>
>> To: <time-nuts at febo.com>
>> Sent:  Tuesday, May 11, 2010 7:02 AM
>> Subject: [time-nuts] Dual  Mixer
>>> The Dual Mixer project is  nearing completion.
>>> Let me refresh every ones memory as to my  goals.
>>> a)  Total cost less than $ 200
>>>  b)  1 E-13 with a one second offset
>>> c)  use parts  attainable by every one
>>> d)  easy to assemble only a few  surface mount parts
>>> e)  a five channel counter that  yields 1 E 15 resolution and
>>> interfaces
>>>  directly to a PC via  RS232 or USB
>>> f)   A  counter that also gives you instant frequency  difference at  
>>> sample rate, not only Allan Variance
>>>  g)  Modular so one can use only the Dual Mixer
>>> h)   Modular so one can use multiple units to do simultaneous
>>>  comparison of
>>> more than two oscillators.
>>>  i)   Isolation between D/M and counter so that the counter can  be
>>> powered
>>> by the PC USB  port
>>> I am happy to report that all goals have  been accomplished, attached
>>> is a
>>> picture of  the D/M, limitation of the file size does not allow me to
>>>  attach
>>> an  actual board picture, but if you contact me  direct I will send
>>> you one,
>>> the  final  board is actually nicer since the first layout had to
>>>  accommodate
>>> several   variances.
>>> The D/M part leans heavy on the  original NIST unit with a few
>>> substitutions
>>>  and recommendations from Bob Camp. Also beside Opto Couplers
>>>  SN65LVDS1's
>>> have  been included for those that want to  use other counting methods.
>>> Selection of  filter  capacitors allow the use at other offset
>>> frequencies such  as
>>> 10 and 100  Hz. The D/M fits in a standard 74 X 111 X  20 mm Euro case
>>> and
>>> the counter can be   stacked below or next to it using the Opto
>>> Isolators  as
>>> the inter connect. The  SYPD-1's fit right on the  board but
>>> connections are
>>> included to use the  HP 10514  A. As a matter of fact removing the HP
>>>  mixer
>>> board from its housing   fits it nicely on the  board and every thing
>>> is still
>>> inside the  housing.
>>> The counter will handle 1 an 10 Hz offset with a 1 E  14 resolution
>>> at 10
>>> Hz. Thanks to Richard Mc  Corkle we have great drawings and code,
>>> available  to
>>> every one.
>>> Code, drawings, list of material  and PC board layouts and its  file,
>>> will
>>>  be available to every one once the project is completed.
>>> I  need help in the following areas
>>> a)  help me create a  nice set of drawings that are computer generated
>>> something I  am not able to do
>>> b) create the computer program that takes  the output of the counter
>>> board
>>> and allows  Allan Variance plots, frequency difference and dual
>>>  temperature
>>> readings and plots using RS232 and  USB.
>>> c) an independent test by a third party.
>>>  As I said previously, I am not getting in the business of  supplying
>>> parts
>>> but will work with people that  will help achieve the three points
>>> listed
>>>  above.  Presently I have boards on order and will have  two
>>> uncommitted board
>>> sets and  probably  also component kits.
>>> Please contact me  directly.
>>> Again thank you Corby Dawson, Richard Mc Corkle and  Bob Camp.
>>> Bert Kehren    Miami

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