[ntp:questions] backup PPS source

Dave Baxter spam at goes.nowhere.com
Tue Apr 13 07:57:14 UTC 2010


In article <82i36jF3r8U1 at mid.individual.net>, snews at lordynet.org says...
> 
> David Lord wrote:
> > 
> > Hi
> > 
> > Latest experiment is to attempt to make a backup PPS source and
> > I've now made a start with a watch xtal oscillator and divider
> > that can be synchronised by a PPS source when present (except
> > I've not yet wired up for synchronisation).
> > 
> >      remote           refid      st t when poll reach   delay   offset 
> >  jitter
> > ============================================================================== 
> > 
> > +GPS_NMEA(0)     .GPSb.           0 l   57   64  377    0.000    1.865 
> >  0.381
> > oPPS(0)          .PPSb.           1 l    -   16  377    0.000   -0.004 
> >  0.002
> >  PPS(2)          .OSCc.           1 l   10   16  377    0.000    1.859   
> > 0.006
> > -k6x400.home.lor 192.168.59.64    2 u    3   64  377    0.951    3.837 
> >  0.447
> > +me6000g.home.lo .MSFa.           1 u   29   64  377    0.905    3.190 
> >  0.451
> > -p4x2400c.home.l 192.168.59.64    2 u   34   64  377    0.832    3.078 
> >  0.343
> > 
> > PPS(2) was time1 fudged to get it < 2ms.
> > 
> > I can see there being problems already with full rotation of trim
> > cap giving about +/- 6 us/s variation and temperature changes
> > have already shown a minor problem (south facing window, very hot
> > day, rapidly going cold tonight). Of course putting the whole
> > oscillator module in a temperature controlled box is in the plan.
> > 
> > Earlier this afternoon I had trimmer set so that offset change
> > between poll periods was < +1us, but that started increasing and
> > change has now reversed direction with offset over last hour
> > having dropped from 1867us, steps at 6min intervals being:
> >   -31 -43 -54 -61 -59 -60 -58 -60 -59 -68 -75 -76us
> > ie total 0.63ms over last hour.
> 
> peerstats for yesterday:
>            ident   cnt     mean    rms     max
> 127.127.22.0     5237   -0.003  0.039   0.217   GPSb pps
> 127.127.22.2     5236  -10.938  4.678  11.263   OSCc pps
> 
> I guess temperature variation over period has been < 15C
> to > 25C.
> 

Take care, varicap diodes have significant tempco's too, and pot's can 
become very noisy after a while, even if you don't physicaly mess with 
them!   We have lots of trouble with multi turn presets that set High 
Voltage PSU levels here at the salt mine.  Seems a common thing, as I 
remember similar things when I worked at Tek UK years (cough... decades) 
back.

Regards.

Dave B(G8KBV)




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