[time-nuts] Segal law: freq difference for GPSDO

Vlad time at patoka.org
Tue Mar 29 20:48:22 EDT 2016



I tried to see the 1PPS on my oscilloscope. Here is the series of 
screenshots from that experiment:

https://www.patoka.ca/OCXO/TBvsSL/

I also tried to catch something using HP5386A. However I was not able to 
measure the pulse.

Regards,
Vlad


On 2016-03-29 18:53, Henry Hallam wrote:
> If you put the PPS outputs of the two GPSDOs into an oscilloscope and
> trigger on the leading edge of one of them, what does the other look
> like?
> 
> Henry
> 
> On Tue, Mar 29, 2016 at 12:56 PM, Vlad <time at patoka.org> wrote:
>> 
>> 
>> Hello,
>> 
>> I am looking for for the advise regarding some strange difference in
>> frequency between of two GPSDO: Trimble Thunderbolt and Datum Starloc 
>> II
>> 
>> Measuring by HP 5386A counter it shows something around 0.0000014 
>> delta.
>> If I connect TB as REF source then I am getting numbers like this:
>> 10.000001396 Mhz
>> If I connect StarLoc II as REF source then I am getting following:
>> 9.999998612 Mhz
>> 
>> May be somebody could recognize, what 10.0000014 Mhz could be used for 
>> ?
>> 
>> TB Lady Heather screenshot
>> http://www.patoka.org/OCXO/TB-LH-Mar.png
>> 
>> Allan Deviation for several hours looks like this:
>> http://www.patoka.org/OCXO/TB-SL.png
>> 
>> 
>> I connected both GPSDO to Rigol DS1102E Oscilloscope to see the phase
>> difference. And its shows me the ellipse which change its orientation 
>> left
>> to right and vice versa.
>> 
>> Its classical case of Segal's law: "A man with a watch knows what time 
>> it
>> is. A man with two watches is never sure". This is exact situation. 
>> Now I am
>> not sure which GPSDO (if any) is more accurate.
>> 
>> I have no third GPSDO (or equivalent) to compare. TB and Starloc 
>> connected
>> to the same GPS Antenna distribution amplifier. So basically both 
>> using the
>> same antenna. Both of them was turned on at relatively the same time 
>> and
>> both was warmed up for few days.
>> 
>> I have a theory, that may be StarLoc II was customized somehow to 
>> produce
>> the freq. slightly different from 10Mhz. But its just a theory.
>> Is it worth to compare 1PPS outputs using something like AD8302 + DAC 
>> + MCU
>> ?
>> 
>> --
>> WBW,
>> 
>> V.P.
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-- 
WBW,

V.P.


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