[evlatests] L302 phase jumps

[jjackson]

I can't see any reason this should be connected to antenna moves or 
location.  The problem seems to be completely related to the timing 
relationship between the two signals (128 MHz and 20 Hz) that go from 
the L305 to the L302. That should be contained entirely within the LO/IF 
rack. The only outside influence I can see affecting it is temperature 
but that is spec'd very tight and seems well controlled.

Swapping out the L302's or L305 could certainly cause it to show up.  It 
seemed likely swapping out the L305's could have caused a bunch of these 
to show up at once - though Vivek claims that doesn't correlate. 
Perhaps a combination of the planned L305 swaps and routine L302 
maintenance swaps explains this.  Historically, synthesizers tend to be 
one of the higher maintenance items in a system like this, so they will 
likely move around frequently. The tests Vivek is working on should be 
useful to check out any L302 for this symptom immediately after it is 
installed.

Cheers,
Jim



Jim Jackson
Project/Lead Hardware Engineer
Very Large Array(VLA) / Very Long Baseline Array(VLBA) radio telescopes
National Radio Astronomy Observatory
1003 Lopezville Rd.
P.O. Box O
Socorro, NM 87801
(575) 835-7132 (W)
(575) 835-0158 (H)
jjackson at aoc.nrao.edu

On 8/4/2014 1:18 PM, Ken Sowinski wrote:
> On Mon, 4 Aug 2014, 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?
>
> I have the impression that much of this is left over from
> the antenna move at the beginnig of Summer.  Vivek does not
> buy that assertion.
>
> Ken
>
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