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

[EWKehren at aol.com]

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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