[ntp:questions] backup PPS source

Dave Baxter 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.

Dave B(G8KBV)




More information about the questions mailing list