[ntp:questions] backup PPS source

David Lord snews at lordynet.org
Tue Apr 13 03:08:32 UTC 2010


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
>> 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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