[time-nuts] FE-5680A Mechanical Question

Bob Camp lists at rtty.us
Fri Jan 13 17:02:31 EST 2012


Hi

What we are talking about is toggling the least significant bit in the DDS to achieve a resolution of less than that LSB. It could be done to a set period (like a PWM) or pseudo  randomly to reduce the noise signature. Either way, roughly a 16 element long "period" should be quite adequate. 7x10^-16 / 16 would give us a 4x10^-14 step and a 2x10^-14 max error.

Bob

On Jan 13, 2012, at 4:30 PM, Don Latham wrote:

> Oh, I hate to be a pedant, but are we talking about dithering, that is
> random perturbations to remove things like hysteresis, or using the
> finite steps as a bang-bang servo?
> Don
> 
> Charles P. Steinmetz
>> Bert wrote:
>> 
>>> wrong there is no DAC involved, it is a DDS
>> 
>> Ahh.  Not so simple, then.  I still don't much like the notion of
>> dithering, but it may be the only alternative.  Or, as has also been
>> suggested here, add a manual C-field adjustment (but that would not
>> change the fact that the RS-232 adjustments would still be ~ 7e-13
>> steps).
>> 
>> Best regards,
>> 
>> Charles
>> 
>> 
>> 
>> 
>> 
>> 
>> 
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> 
> 
> -- 
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> are as significant as experiment, for thence comes quiet to the mind."
> R. Bacon
> "If you don't know what it is, don't poke it."
> Ghost in the Shell
> 
> 
> Dr. Don Latham AJ7LL
> Six Mile Systems LLP
> 17850 Six Mile Road
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> 
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