[time-nuts] GPS 1 PPS accuracy limits

Bob Camp lists at rtty.us
Wed Apr 21 07:29:11 EDT 2010


Hi

Does accuracy include temperature change over -55 to +85 C at a 1 C / minute rate?

Is accuracy measured after a 5 minute cold start at any temperature?

Does accuracy include a contribution internal to the synthesizer (like DDS step size)?

Is accuracy simply "where we set it when we shipped it"?

There are *lots* of variations to this particular spec....

Bob

On Apr 20, 2010, at 5:59 PM, SAIDJACK at aol.com wrote:

> Hi Magnus, Life speed,
> 
> what does accuracy mean? Average (rms, 1-Sigma) frequency accuracy? If yes, 
> over what time frame is the average?
> 
> Or is this the peak to peak allowable deviation? Over what temperature  
> range, and after how long of a warmup?
> 
> To give you an example, a typical Fury desktop unit with DOCXO is  capable 
> of better than 2us holdover drift per day after 3 to 5 days of constant  
> operation.
> 
> That equates to an average frequency accuracy over one day without GPS of  
> <2.3 x 10^-11.
> 
> With GPS the accuracy on average is better than 2E-012 after about an  hour 
> or so averaging.
> 
> bye,
> Said
> 
> 
> 
> 
> In a message dated 4/20/2010 13:07:53 Pacific Daylight Time,  
> magnus at rubidium.dyndns.org writes:
> 
> life  speed wrote:
>> Time Nuts;
>> 
>> I have a customer request for  a microwave frequency synthesizer with 
> extreme accuracy requirements;
>> 4 X 10^-11, or 0.04 PPB.  Obviously this is way out of quartz oscillator 
> territory.
>> Is GPS 1 pulse-per-second useable, or do they need an  atomic clock?
>> Maybe they don't realize what they are  spec'ing.
> 
> I really think you should ask them to motivate themselves on  that spec, 
> the intended use etc. They can certainly get a spec like that,  but is it 
> what they need?
> 
> You certainly want something like a GPS  clock to feed that thing if they 
> really need that level of accuracy. Or do  they only need that level of  
> resolution?
> 
> Cheers,
> Magnus
> 
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