[time-nuts] FE-5680A Mechanical Question

EWKehren at aol.com EWKehren at aol.com
Fri Jan 13 18:26:27 EST 2012

The controller looks at the 10 MHz from the Rb and a 1 Hz signal from  
either a GPS or a tbolt. Over the years I have been very happy with the Shera,  
except for the DAC. I control my Rb,s to .1 C.
In a message dated 1/13/2012 6:06:05 P.M. Eastern Standard Time,  
albertson.chris at gmail.com writes:

On Fri,  Jan 13, 2012 at 2:42 PM, Jim Lux <jimlux at earthlink.net> wrote:
>  On 1/13/12 2:33 PM, Chris Albertson wrote:
>> On Fri, Jan  13, 2012 at 2:19 PM,<EWKehren at aol.com>  wrote:
>>> Are we not overdoing it. 7E-13  for $15 KISS, and if you want to go 
>>> that use a $ 30  analog version.
>>> Looking right now at 1 E -14, I do se  temperature influences, with my
>>> heat
>>> sink  stable to .1 C. Mainly due to the fact that is only one side of  
>>> unit  and it is clearly designed to use all sides for  heat dissipation.
>> Technical question, how  does one measure 1E-14 changes in frequency?
>> I'm  thinking about building a controller and of course you can't
>>  control what you can't measure.  But at that small level what do  you
>> use for a reference?
>  Your other sources.  Seriously..
> Of course, the man who has two  clocks doesn't know what time it is.
> If you have 3 sources,  you can do three cornered hat type measurement
> comparisons, for  instance.
> Typically, you might have clocks of various kinds.  For instance, a nice
> quiet quartz oscillator has great phase  noise, but does drift with time 
> temperature. So you could use that  to measure the phase noise of 
> with not so hot  performance.

OK, in general I understand.  But now we are talking  about a $15
controller that needs to make a decision wetter to increment  the DDS
by 7E-13 or not.  What is this controller looking  at?

People are already asking if people can write software and making  PCB
designs but first one needs to know basic things like:
(1) what to  use as a reference?
(2) what kind of phase detector has the sensitivity to  enable
decisions at the e-13 level or e-14 level.
(3) What time  constants and loop gains would be reasonable
(4) does the controller need  input for temperature?
(5) should the controller look at the saw tooth  correction from the GPS
(6) seems that a Kalman filter would help?   Seems it could if you have
a good temperature and aging model.

Lots  more I'm sure but basic requirements are needed before any design
can  begin.   Hence my plan to use a desktop computer as  the
controller.    I suspect the first few prototype solutions  will not
work well.

Chris Albertson
Redondo Beach,  California

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