[time-nuts] Re: Dumb nooby question ... sorry all

[Nick]

On 19/03/2022 14:13, Bob kb8tq wrote:
> Hi
> 
> The PPS out of a “normal” GPS module is derived from a free running
> TCXO. The edge it puts out is only approximately correct. The magic
> term for this a “sawtooth” since the departure from correct phase can
> look a bit like a sawtooth when you plot it.
> 
> Many modules provide a “sawtooth correction” output as part of the
> serial stream. This lets a GPSDO work with a more accurate representation
> of what’s happening. Data collection wise, if you run a time interval counter
> to capture the OCXO vs GPS info, you *could* fold that information into
> your data plot.
> 
> A sawtooth of 20 to 40 ns is not at all uncommon. As time has marched
> on, the clock rates internal to the GPS modules have gotten higher. That
> has dropped the peak to peak a bit.
> 
> So, simple answer: what you see is normal.
> 
> Bob

Bob, thanks for that.

A bit of a play today & comparing the Leo Bodnar 10 MHz against that 
coming out of my GPSDO I see only about 2-3 ns jitter - more like I 
expected and with a frequency ever so, ever so, slightly higher than the 
leo bodnar.  I know that it actually tells me nothing other than one or 
the other (well both actually) are wobbling about.

So all in all - happy!

Many thanks

Nick
M0HGU


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