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-boun...@febo.com [mailto:time-nuts-boun...@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 > -- > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
