[evlatests] Master LO frequency references and the 1.7ms discrepancy

[Bryan Butler]

or we could have our maser back...


Walter Brisken wrote, On 4/18/13 15:21 :
>
> Are you sure that it is not running on a Mickey Mouse watch from a vending
> machine?  That drift rate sounds horrid!  Maybe we could upgrade to a Seth
> Thomas metronome.
>
> -Walter
>
> On Thu, 18 Apr 2013, Keith Morris wrote:
>
>> Yes, my mistake.  I remeasured this morning and I find a rubidium drift
>> rate of about 100us per day.
>>
>>
>>
>> Vivek Dhawan wrote:
>>> A short VLA-PieTown fringe test was done last night.  I can confirm that the
>>> 1.7ms is gone, the VLA was at ~2.5usec offset from UT.
>>>
>>> There is however a fierce rate of drift, ~5Hz at C band or  10^-9, so about
>>> 10 times more than Keith's 9.8us/day
>>>
>>> There are also various warts on the phase - and a lower fringe amplitude,
>>> though I have not yet done a careful comparison - from the short-term
>>> (seconds) instability of the rubidium.
>>>
>>>
>>> On Thu, April 18, 2013 07:30, Keith Morris wrote:
>>> | As it stands now, the L356 firmware version that is installed at the site
>>> | accurately measures the drift, but not the offset, between the GPS and the
>>> | synthesized pulse.  We have been testing a new firmware version in the lab
>>> | in which we attempt to address the offset problem, but it is not yet ready
>>> | to deploy.
>>> |
>>> |
>>> |
>>> |
>>> |> It seems to me that the monitor point design must be changed to
>>> |> measure the lag between the L356 and the GPS, so this doesn't happen
>>> |> again.
>>> |>
>>> |>> We located the source of the 1.7 millisecond timing discrepancy.  The
>>> |>> GPS
>>> |>> 1PPS signal and the 1PPS signal generated in the L356 were
>>> |>> mis-synchronized by exactly this amount, with the L356 lagging in
>>> |>> time.
>>> |>> This is due either to the L356 having been synchronized to the wrong
>>> |>> mark,
>>> |>> or not having been synchronized at all.  We resynchronized the two
>>> |>> pulses
>>> |>> this morning at 11am.
>>> |>>
>>> |>> Then, at 11:40am, we switched the master frequency reference from
>>> |>> Hydrogen
>>> |>> Maser to Rubidium, as planned.  The PPS that is synthesized from the
>>> |>> Rubidium 5MHz is drifting relative to the GPS at a rate of about 9.8
>>> |>> microseconds/day.
>>> |>>
>>> |>> _______________________________________________
>>> |>> evlatests mailing list
>>> |>> evlatests at listmgr.cv.nrao.edu
>>> |>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>>> |>>
>>> |>
>>> |>
>>> |
>>> |
>>> | _______________________________________________
>>> | evlatests mailing list
>>> | evlatests at listmgr.cv.nrao.edu
>>> | http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>>> |
>>>
>>
>>
> _______________________________________________
> evlatests mailing list
> evlatests at listmgr.cv.nrao.edu
> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>