[ntp:questions] backup PPS source
snews at lordynet.org
Sun Apr 11 23:20:43 UTC 2010
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
+GPS_NMEA(0) .GPSb. 0 l 57 64 377 0.000 1.865
oPPS(0) .PPSb. 1 l - 16 377 0.000 -0.004
PPS(2) .OSCc. 1 l 10 16 377 0.000 1.859
-k6x400.home.lor 192.168.59.64 2 u 3 64 377 0.951 3.837
+me6000g.home.lo .MSFa. 1 u 29 64 377 0.905 3.190
-p4x2400c.home.l 192.168.59.64 2 u 34 64 377 0.832 3.078
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
I also keep googling for rubidium sources but not found any
within my budget, cheapest I've found (new) starting at ukp 900.
More information about the questions