[time-nuts] Long period variation of GPS PPS timing?
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.
(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,
> Thanks again, I'll report back when I find the problem.
> Paul Nicholson
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