[evlatests] L-band performance

[Chuck Kutz]

As discussed in the EVLA Coordination meeting yesterday, the L-bands in
antennas 12,13,18,23,and 16 have LNAs that have manifested anomalous
behaviors since the 2nd of December, 2011. This does not mean that the
receivers are unusable, please read Bob Hayward's message regarding this
issue that he posted yesterday.

A complete survey of all L-bands, revealed that antennas 5,7 and 26 need to
be added to the list.  Note, antenna 7 uses a model 350 refrigerator not a
model 1050.

As an aside,  a survey was performed of all the EVLA compliant S-band,
C-band and X-band receivers; all of these receivers are observed to be
presenting nominal parameters.

The Front End group will endeavor to clear up these issues as fast as we
can, but this is going to take a little time. Each receiver's prioritization
for repair work will be based on the functionality of any given receiver
(worst performers first). Since there are no spare EVLA L-band receivers
until the array is fully populated, the array will be less the one receiver
while it is being repaired. 

If we tried to skip an upgrade of an L-band receiver(s), the outcome would
be to negatively impact the S-band receiver schedule. We reuse the interim
L-band receiver dewar for the S-band.


-----Original Message-----
From: evlatests-bounces at nrao.edu [mailto:evlatests-bounces at nrao.edu] On
Behalf Of Rick Perley
Sent: Monday, January 09, 2012 3:26 PM
To: evlatests at aoc.nrao.edu
Subject: [evlatests] L-band performance

    As part of debugging the tendency for my scripts to collapse the 
correlator, another 'flux density' test script was run today.   This 
script includes L-band, so I took a careful look at the data, given Chuck's
report this morning of some serious issues with the L-band receivers.
    The situation isn't nearly as dire as Chuck's report seemed to indicate:

    1) Antennas 11, 17, and 19 were out of the array.
    2) ea18 gives essentially no fringe power at any of the four subbands. 
    3) ea26 is similarly weak, on RCP only.
    4) ea23 is also very weak, on LCP only. 
    5) ea13's fringes are down by about half in RCP. 
    6 Three other antennas give weaker-than-expected fringes on single
IFs:  ea07A, ea04A, and ea15C.  However, these might perhaps be low power
levels specific to a single IF. 
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