[GPS_Standard] GPS Jitter.

[Glenn Elmore]

Stig

Yes, summing and voting would seem to me to be similar to integrating 
and differentiating. Voting effectively throws away some long term 
information. I think I read (somewhere) that people are finding summing 
to be the more accurate mode.

Multiplying the reference doesn't improve PPM but it could reduce 
jitter-counts/total-counts-per-unit-time.  This would have the advantage 
of allowing higher DFLL loop bandwidth because less DFLL-jitter-noise 
would need to be filtered and could potentially allow the PIC to do more 
to clean up the (short term) performance of a reference oscillator.

So much depends upon the quality of the reference to be disciplined. If 
it already has very good short-term stability, there's probably not much 
lost by using the PIC board and software as-is. As you say, it certainly 
is low investment and can serve to get things synchronized. That's all 
that is necessary for many applications. However, perhaps some 
improvements could allow relatively poor (cheap!) reference oscillators 
to be improved to more nearly the point of a really good oscillator.

very 73,
Glenn   n6gn

Stig OZ3XO wrote:
> My mistake, you are right, the sampling time is only 16 sec, with a 16 
> sec DAC rest time, starting a new count every 32 sec, ( that's what I 
> remembered ).
> The PIC has the two averaging modes available as the summing mode and 
> voting mode, so has to be possible to adapt to averaging out the 
> jitter of the system.
>  
> You are right about using a higher frequency, and using the controlled 
> oscillator might be a good idea, but multiplying a frequency, still 
> give the same PPM error to the system.
>  
> I am working with commercial V-Sat transmitting on 14,5 GHz, with as 
> low speed as 32 Kbps, and HF Maritime DSC Modems, and I found out, 
> that for commercial use, the stability don't has to be that high, but 
> for very narrow band communication in very high frequency's, it will 
> still call for high stability.
>  
> So it will never be perfect, but near perfect for only a fraction of 
> the investment might just be what is needed.
>  
> Best 73
> Stig - OZ3XO
>  
>
>