[evlatests] L302 phase jumps

[Rick Perley]

     From L-band data taken 27 June, I can assert the following. Note -- 
these data were taken in a cyclical mode -- cycling through L, S, C, and 
X bands.

     1) ea27 (and only ea27) was doing the 'phase jump' thingie, meaning 
that with every L-band calibration, the A and C IF had a (very) 
different phase.  IFs B and D were stable.
     2) The jumps and A and C were *identical*.  (That is, the A-C phase 
was as stable as any other normal antenna).

     I haven't been able to check behavior in the other bands yet. If 
this is important, I'll bump this priority ...

     Rick

On 08/04/2014 11:02 AM, Keith Morris wrote:
> Vivek:
>
> Do we have any sense of when these symptoms first appeared?  In other 
> words, is there evidence that the "phase jumps" predated the last 
> array configuration change?
>
>
>
> On 8/1/2014 3:55 PM, Vivek Dhawan wrote:
>>
>> Here is a list of problem units from a test done July 31 evening.
>> I'm working to make the test ~10 minutes, we can run it often.
>>
>> ea11  L302-3,  L302-4.                  ea12  L302-2.
>> ea15  L302-3.                           ea22  L302-1,  L302-4.
>> ea27  No L302 problems found. But there were delay jumps yesterday.
>>        This makes a differential phase jump on an IF pair (deltaA
>>        does not equal deltaC).  An LO jump makes identical phase
>>        changes on both of a pair.
>>
>> I am pretty sure after talking to various engineers that this is the
>> '128MHz cable adjustment' problem, where the relative timing of the
>> 128MHz and 20Hz edges changes with time or temperature. Sometimes it
>> is the 20Hz into the L302 which is weak or jittery. Both these things
>> should be checked.
>>
>> I had a thought that it may be triggered by something else, but came
>> up empty on 2 counts:
>>
>> 1. No correlation with L302-x MIB versions (from Hichem.)
>>
>> 2. L305 modules are being deployed with updated FPGA firmware to change
>>     the DTS Timecode from 19.2 to 20 Hz. Below is the list from Leon, I
>>     see no correlation with antennas or dates of deployment.
>>
>>     ea04 - no date recorded.               ea13 - 5/28/2014
>>     ea16 - <5/15/2014   ea14 - 6/11/2014   ea06 - 6/19/2014
>>     ea10 - 6/19/2014    ea12 - 7/2/2014    ea23 - 7/9/2014
>>     ea25 - 7/23/2014    ea05 - 7/10/2014
>> ---------------------------------------
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