[ntp:questions] backup PPS source
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)
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