[ntp:questions] backup PPS source

G8KBV dave at g8kbv.removethis.demon.co.uk
Mon Apr 12 18:37:15 UTC 2010


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
> within my budget, cheapest I've found (new) starting at ukp 900.
> 

Sounds like a candidate for membership of the "Time Nuts" mailing list!
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

:)

(The certificate is self signed.)

Dave B.




More information about the questions mailing list