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

[Keith Morris]

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.
> |>>
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> |>
> |>
> |
> |
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> 

-- 
Keith Morris
National Radio Astronomy Observatory
1003 Lopezville Rd.
Socorro, NM 87801
575-835-7060 (phone)
575-835-7027 (fax)