[time-nuts] PRS-10 input and output calibrations

bg at lysator.liu.se bg at lysator.liu.se
Sun Apr 22 20:47:40 UTC 2012


With factory default settings with 2 PRS-10s, connecting 1PPS_out from one
unit to 1PPS_in on the other, would not align the 1PPS_out pulses. They
were off by several hundred of ns. It was probably an operator error
somewhere. We just did not find the error in the time frame we had
available.

--

   Björn


>   Björn, what do you mean with "We never got one to track the other in a
> reliable way"?
> Thai is, how can it be that a PRS10 cannot track another PRS10? What do
> you
> get when trying to track one with the other?
>
> On Sun, Apr 22, 2012 at 8:44 PM, Poul-Henning Kamp
> <phk at phk.freebsd.dk>wrote:
>
>> In message <4F93F032.2040608 at rubidium.dyndns.org>, Magnus Danielson
>> writes:
>>
>> >The input calibration would be something in the similar way,
>>
>> What I did:
>>
>> Detune an OCXO slightly (I actually have a 9.99997 MHz OCXO from
>> IsoTemp), feed it to PPSDIV, disable the discipline code in the
>> PRS10, collect the measured input time stamps over some hours.
>>
>> Either you get a nice ramp, or you get som kind of demented staircase,
>> in which case you try to figure out which of the calibration constants
>> to mess with.
>>
>> An alternative is to feed the PRS10 output to a HP333x Synthesizer
>> and have that generate your 10-epsilon MHz for the PPSdiv.
>>
>> This general "vernier" method can be used to measure all sorts of tricky
>> stuff, from interrupt latencies in operating system kernels to
>> stuff like the above.
>>
>> --
>> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>> phk at FreeBSD.ORG         | TCP/IP since RFC 956
>> FreeBSD committer       | BSD since 4.3-tahoe
>> Never attribute to malice what can adequately be explained by
>> incompetence.
>>
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