[ntp:questions] backup PPS source
spam at goes.nowhere.com
Tue Apr 13 07:54:34 UTC 2010
In article <82i5hhFekiU1 at mid.individual.net>, snews at lordynet.org says...
> G8KBV wrote:
> > In article <82f3qcFg17U1 at mid.individual.net>, snews at lordynet.org says...
> >> 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.
> >> The temperature swings today have also has adverse effect on the
> >> three peers shown that on a good day can all be < 500us.
> >> Any hints/tips welcome, I'm also considering an oscillator using
> >> an AT cut xtal but design for that is considerably more complex,
> >> however it's then a possibility to convert the HF to be used as
> >> system clock.
> >> I also keep googling for rubidium sources but not found any
I bet the first 'birds nest' version works better. Nice job sir.
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