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.
That level of drift is much better than I'd expected so
I'll move on to next stage as soon as I have the temperature
control sorted (peltier device) and for tuning replace
trimmer with varicap and use a 10t pot to set frequency.
David
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