[evlatests] VLA System health

[Ken Sowinski]

On Wed, 6 Mar 2013, Bryan Butler wrote:

>
> i'm curious why our normal stress test isn't finding these issues?  i
> thought that was the whole point of those observations.

1.  I don't think the stress test makes any use of P_sum or P_diff.

2.  Problems are transient.  Rick and the stress test provide a snapshot
of what is happening at a single moment.

3.  Related to 2. the stress test is run infrequenctly, and only when we 
think things are up to snuff after (or before) a maint day.

Ken



> Rick Perley wrote, On 3/6/13 12:00 :
>>      From the short test, preparing for the 'flux densities', I find:
>>
>>      1) L-band:  All antennas o.k., all PDifs are plausible.
>>
>>      2) S-band:  No fringes or PDif from ea03 -- presumably, the receiver
>> is not yet in?  ea06, on IF 'A' gives a sinusoidally varying PDif of 20%
>> amplitude, and 1 minute period.  (It has always done this).
>>
>>      3) C-band:  All antennas fringe.  ea14 gives a negative, or
>> extremely weak, PDif on all IFs.
>>
>>      4) X-band:  No fringes from ea20.  PDif = 0 from ea02 and ea20.
>> Both antennas show healthy PSum.  ea14 has very low PDif, but o.k. PSum.
>>
>>      5) Ku-band:  No fringes from ea23, but PSum and PDif both normal.
>> ea10 is showing large gain changes from scan to scan (0.7 dB).  All
>> others o.k.
>>
>>      6) K-band:  No fringes from ea23, and PDif is very small (Tsys
>> claimed to be 500K).  Ea07 has system temeprature of about 300K.  All
>> others o.k.
>>
>>      7) Ka-band:  No fringes from ea23, and PDif equal zero on all IFs.
>> (Or, Tsys >1000 K).  All others o.k.
>>
>>      8)  Q-band:  No fringes from ea 23 on IFs B and D (and PDif = 0).
>> Fringes seen on IFs A and C.
>>                           ea08 gives zero PDif on all IFs.
>>                           Very high Tsys (> 200K) on ea 7 and ea18.
>>
>>      The lack of fringes from ea23 for Ku, K, Ka and Q band seems to
>> indicate a problem with the UX downconverter
>>
>>
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