[time-nuts] FE-5680A Mechanical Question

David davidwhess at gmail.com
Thu Jan 12 11:55:46 EST 2012

I thought maybe they applied some kind of complicated phase locked
loop frequency and phase addition or subtraction to the RbO output.  I
did not know that the RbO itself was so easily tuned.

A tuning loop for the DDS is how the noisy design worked.  It is not
clear to me if the phase noise was caused by low DDS tuning word
resolution or the DDS itself.  The SRS design locks the RbO to the GPS
1PPS with a time constant of up to 18 hours and then phased locks an
OCXO to generate the 10 MHz output.

Oddly enough, I ran into a similar problem in lack of tuning
resolution when I designed the source for the frequency to voltage
converter of my napkin GPSDO.  I ended up with a reciprocal DDS (as
best as I can describe it) to generate a low frequency high resolution
frequency source.

On Thu, 12 Jan 2012 10:43:15 -0500 (EST), EWKehren at aol.com wrote:

>Bringing out the C field in my estimation does not effect long or short  
>term. External magnetic field I think is a joke. An other option is a loop 
>that  generates a tuning word for the DDS but that means your steps are 7 E-13.
>Bert Kehren
>In a message dated 1/12/2012 10:34:10 A.M. Eastern Standard Time,  
>davidwhess at gmail.com writes:
>I was  more interested in the technical details of how to adjust the
>output of a  RbO without sacrificing the short and long term stability.
>I have seen a  few designs that used a DDS to generate the 10 MHz
>output which lends  itself to this but they all suffer from DDS and
>tuning noise.  I see  now that the RbO can be adjusted with an external
>magnetic field.
>On  Thu, 12 Jan 2012 07:34:44 -0600, "J. L. Trantham"  <jltran at att.net>
>>I have been  following discussions on the list about a GPSDRbO for a year  
>>so.  Some interesting challenges and probably best implemented  in a 
>>environment rather than portable operation but as best I  can tell, it 
>>require a very stable and good antenna location,  stable and clean power, 
>>I was thinking of using something like an  LPRO-101 with an Ext C Field
>>input, a Shera type controller, and a GPS  timing receiver, though, I 
>>there are likely to be some  'multi-tasking' receivers out there that will
>>look at several sources  including GPS, GLOSNASS, etc.
>>While the project might be fun,  for portable work, it is likely far easier
>>and probably just as good  (almost), to use a Tbolt.
>>In any event, something to think  about for the future.
>>-----Original  Message-----
>>From: time-nuts-bounces at febo.com  [mailto:time-nuts-bounces at febo.com] On
>>Behalf Of David
>>Sent:  Wednesday, January 11, 2012 11:12 PM
>>To: Discussion of precise time and  frequency measurement
>>Subject: Re: [time-nuts] FE-5680A Mechanical  Question
>>How would a GPSDRbO work?  Phase lock the  DDS output to the GPS? Phase 
>>a VCXO to the GPS and then phase lock  to the RbO on loss of GPS lock?
>>On Wed, 11 Jan 2012 22:55:58  -0600, "J. L. Trantham"  <jltran at att.net>
>>>Bill, Brian, Bill, and  Peter,
>>>Thanks for the info.  All I need now is a  'project' to incorporate the 
>>>unit into.
>>>In  the back of my mind, I have the thought of a 'box' that will be  
>>>battery powered or 110 VAC powered (perhaps with an internal SLA  
>>>battery) and include a GPSDO and Rb unit (possibly a GPSDRbO) for  the 
>>>purpose of a 'reference' for portable operation in the  microwave  
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