G8KBV wrote:
In article <82f3qcfg1...@mid.individual.net>, sn...@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
Have a laugh on me
MSFa the Conrad module is the small green pcb with blue terminal
block, 77.5kHz xtal replaced with 60kHz and using LW aerial from
Rapid.
http://www.lordynet.me.uk/pub/ntp/m0041359.jpg
32768Hz oscillator (cmos 4007 + watch xtal) and divider
(74HCT4060 + 74HCT74) for 2Hz, 1Hz and 0.5Hz out.
http://www.lordynet.me.uk/pub/ntp/m0041360.jpg
David
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