[time-nuts] New Trimble timing products

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon May 21 22:44:08 EDT 2007


Didier Juges wrote:
> Dr Bruce Griffiths wrote:
>   
>> Didier Juges wrote:
>>   
>>     
>>> Sorry, it's not 15nS rms, it's 15nS at 1 sigma.
>>>
>>> Didier KO4BB
>>>   
>>>     
>>>       
>> Didier
>>
>> Surely the standard deviation (1 sigma) and the rms values are identical?
>> Specifying 1 sigma is perhaps intended to signify that the timing error 
>> is stochastic.
>>
>> Bruce
>>   
>>     
> Bruce,
>
> Not knowing how it is measured and the nature of the noise, I realized I 
> had *assumed* rms and 1 sigma to be the same, but in fact I was not sure.
> The data sheet does say "at 1 sigma", so I wanted to be accurate and not 
> make assumptions, this is time-nuts after all :-)
>
> Let's be honest, if I had not corrected myself, you would probably have 
> commented, and rightfully so, that the data sheet actually said "at 1 
> sigma" :-)
>
> I am trying to learn, I am just a little slow...
>
> Didier
>   
Didier

Oops, if however the error has a non zero mean then the rms and 1 sigma 
values are not identical.
Such a systematic offset can arise from antenna, receiver and cable delay

Bruce





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