[time-nuts] Long period variation of GPS PPS timing?

Matthew Kaufman matthew at matthew.at
Thu Jul 1 17:11:50 UTC 2010


What is the soundcard sample rate? This feels like an artifact of  
sample phase vs. pulse phase to me.

Matthew Kaufman

(Sent from my iPhone)

On Jul 1, 2010, at 9:06 AM, Paul Nicholson <vlf0308 at abelian.org> wrote:

> Thanks all for the various replies, on and off list.
>
> John WA4WDL wrote:
> > Perhaps you should use only the leading edges for the
> > pulse-to-pulse interval measurement.
>
> Yes, I'm just using the leading edge, turning it into a pulse
> using a couple of RC networks, slowing the rise and fall enough
> to give a nice shape for accurate locating of the centroid.
>
> Antonio CT1TE wrote:
> > I can send you the yesterday record of my GPS TBolt #2 against
> > DCF77, which apparently doesn't show any periodic phase
> > variation.
>
> Thanks for the offer.  Hold on that, I'll assume for now that
> this slow cycle is not ionospheric.
>
> Rob Kimberley wrote:
> > I'm assuming your location is fixed, and you are tracking
> > sufficient SVs,
>
> Fixed.  Maybe I can relocate the GPS antenna for a better view of
> the sky.
>
> Peter Vince wrote:
> > I don't believe that cyclic variability is GPS - I've not
> > noticed such a thing on any of the systems I monitor.
>
> Thanks, that's very helpful.  Knowing that this is not normal
> behaviour for GPS timing means that I can set about tracking down
> a system fault.
>
> There are a few things I can think of to check.  The cycle must
> correlate with something - soundcard rate, temperature, CPU clock,
> etc.  It is pretty consistent, here is a bit more of MSF 60kHz
> and also DCF at 77.5kHz,
>
> http://abelian.org/vlf/live/pp100701msfc.png
> http://abelian.org/vlf/live/pp100701dcfc.png
>
> Thanks again, I'll report back when I find the problem.
> --
> Paul Nicholson
> http://abelian.org
> --
>
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