[time-nuts] FE-5680A Mechanical Question

Bob Camp lists at rtty.us
Thu Jan 12 13:00:15 EST 2012


Hi

The 7x10^-13 step size is a direct result of the DDS chip they chose. If you
want to keep the cost down, there aren't a lot of choices...

If (and that's a big if) you can dither at ~10 steps a second, you could see
the +/- 3x10^-13 at 0.1 second and be down to +/- 3x10^-14 at 1 second. The
ADEV on the part is likely 3 or 4x10^-11 at 0.1 second. The dither would be
1/100th of the noise that's already there.... 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chris Albertson
Sent: Thursday, January 12, 2012 12:44 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] FE-5680A Mechanical Question

On Thu, Jan 12, 2012 at 9:20 AM, Bob Camp <lists at rtty.us> wrote:
> Hi
>
> I think it would be worth the effort to try dithering the DDS commands
into
> the Rb while measuring ADEV. You *might* find that you can do it with
little
> or no impact on the unit's stability. If so it takes out some modification
> effort and should make the controller cheaper.

The step size on the DDS is just over 5E-13.  This means a worst case
error of about 3E-13.   It could very well be that the Rb oscillator
can't be tuned any better than that. and RS232 is as good as you can
get.        Good chance that the engineer who picked the 5E-13 step
size pick it for good reason
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of EWKehren at aol.com
> Sent: Thursday, January 12, 2012 10:43 AM
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] FE-5680A Mechanical Question
>
> 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>
> wrote:
>
>>David,
>>
>>I have been  following discussions on the list about a GPSDRbO for a year
> or
>>so.  Some interesting challenges and probably best implemented  in a
> 'stable'
>>environment rather than portable operation but as best I  can tell, it
> would
>>require a very stable and good antenna location,  stable and clean power,
> and
>>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
> suspect
>>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.
>>
>>Joe
>>
>>-----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
> lock
>>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>
>>wrote:
>>
>>>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
>>>regions.
>>
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>>
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-- 

Chris Albertson
Redondo Beach, California

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