[time-nuts] GPS and Rubidium frequency standards and noise question (new...

[Bob Camp]

Hi

I think that if you switch to an averaging of a few seconds from "per pixel" the plot of frequency difference will look a bit different. The phase perturbations from DDS will still be there, and they are an issue. They just many not be as dramatic as that plot implies.

Bob

On Jun 3, 2012, at 8:14 PM, EWKehren at aol.com wrote:

> The  FEI 5680A we recently discussed uses the DDS to generate  part of the 
> excitation to the filter. Fine stepping the excitation  frequency.  The 
> output is taken off the 60 MHz and divided by 6. I noticed  the changes when 
> doing my aging tests but some disagreed. The attached I think  it is from John 
> Miles shows it very clearly and what is needed is a clean up  loop with some 
> thing like a MV89. I think the source is the control loop which  most 
> likely is digital. FRS and FRK are analog but will also improve with an  external 
> OCXO.
> Bert Kehren
>>> The FEI-5680A Rubidium that we discussed here  some time ago has a much
>>> worse phase noise plot of course, because  the 10MHz is generated 
> digitally
>>> through a DDS, not a 10MHz crystal  oscillator..
>>> 
>> There is a version that generates 10MHz  directly through DDS, but the 
> particular version we recently discussed a lot  about generates the 10MHz 
> signal from a 60MHz oscillator, and the DDS is used  for generating the 
> ~5.3125MHz signal for mixing with the 114th harmonic of the  60MHz to obtain the Rb 
> resonance frequency.
>> 
>> I don't remember if  someone did a comparison in PN performance between 
> the two FE-5680A  flavours.
>> 
>> Regards,
>> 
>> Javier
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