[time-nuts] GPS PPS smoothing article

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 11 17:04:54 EDT 2010


SAIDJACK at aol.com wrote:
> I see other problems in the paper as well, for example why did they just  
> plot a time-domain plot of before and after which doesn't really say much. It 
>  "looks" less noisy, but that doesn't mean anything. The peak to peak is 
> very  similar.
> 
> Instead they should have put that data into the freeware plotter, or  
> Stable-32 etc, and shown ADEV plots that can actually discern between  before and 
> after.

That they didn't use a time-interval counter but scopes kind of 
indicates that they may not have been sufficiently equipped for this task.

> Also, as Matt mentioned if they do only have two dis-similar scopes, then  
> they could have swapped the scopes, and do an interpolation between the two  
> datasets.

At least they could have swapped scopes to (hopefully) show that it did 
not make any major shift in results. If they did get shifts, then they 
would have concluded that the approach was not sufficient, reported that 
and then continued with another approach.

> Or they could have used the "trigger" input in the 500MHz scope (it has one 
>  for sure) for the reference, and channels 1 and 2 for the before/after  
> sources.

What if they would have used any of a line of suitable time-interval 
counters?

They should have done their ADEV and TDEV plots for sure. Implementing 
them for any of their available sources should not be too hard either.

They do tell that they are using a 100 MHz clock if you look at page 3, 
column 2 (with a line-break between 100 and MHz so it is a little hard 
to spot).

Cheers,
Magnus




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