[evlatests] phase jump phenomonology

[Rick Perley]

    Permit me to emphasize a point:  Ken found an old message of mine, 
from August, noting precise 180 degree jumps between scans (in 
holography mode at a single frequency) when the BW was 12.5 MHz, and 90 
degree jumps when the BW was 6.25 MHz.  This precise class of jumps were 
not seen after September (I was in Australia for two weeks from 
mid-Sept. to early Oct.) -- but were replaced with others.
    Last Friday, I pounded away on holography, and *no* phase jumps of 
any kind were found. 
    On Wednesday, I tried various observations at L-band -- at a BW of 
12.5 MHz -- and the 180 degrees jumps are back.  I would guess something 
was changed between Friday and Wednesday which brought back an old 
nemesis ...

    Rick

   

Ken Sowinski wrote:
> Below is the email describing changes to the source of 5 MHz for
> the EVLA hardware.  It is a remarkable coincidence that Rick
> reported many examples of 180 degree phase jumps before Sept 13,
> and now again after Jan 29.  In between he more than once remarked
> plaintively, 'what have we done to fix it' in response to the
> lack of phase jumps of this type.
>
> Between those two dates there are many reports from both Rick
> and Vivek describing phase jumps which agreed fully in character
> with those measured at the VLA in the two L350 test setup last month.
> Those phase jumps were not seen before Sep 13; and have not been seen
> since Jan 29, though that has only been a few days.
>
> I offer no explanations, but want to make sure that everyone is
> aware of these coincidences.
>
>
>
>
> On Wed, 13 Sep 2006, Jim Jackson wrote:
>   
>> The following changes have been made to the EVLA antennas today:
>>     
>
>   
>> The EVLA antennas have been switched over to the 5MHz signal from the VLA
>> LO racks.  This will allow the EVLA to follow the VLA should a backup
>> references be connected in the event of a MASER outage.  This added 20-30ft
>> of cable to the 5MHz timing to the EVLA. We're not sure whether or not this
>> will effect delays  but it could.
>>
>> Jim
>>
>>
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>>     
>
>
> On Mon, 29 Jan 2007, Rob Long wrote:
>   
>> Date: Mon, 29 Jan 2007 18:24:38 -0700
>> From: Rob Long <rlong at nrao.edu>
>> To: evlatests at nrao.edu
>> Subject: [evlatests] EVLA hardware
>>
>> The L350 is being phase-locked directly from the spare Maser output 
>> again.  We can monitor for a while and see if the global (EVLA) phase 
>> jumps are gone or not.
>>
>> Rob
>>
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