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

J. Forster jfor at quik.com
Thu Jul 1 16:41:53 UTC 2010


Is the environment heated or have AC? With a period of about 40 minutes
I'd look for something thermal.

FWIW,

-John

============


> Hi
>
> What kind of caps are you using in the network? Some of the stuff you get
> these days has really awful TC.
>
> I'd put a heat gun on your R/C networks and see what happens...
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Paul Nicholson
> Sent: Thursday, July 01, 2010 12:07 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Long period variation of GPS PPS timing?
>
> 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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