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 <[email protected]> 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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