[evlatests] calibrator flux survey preamble

[Ken Sowinski]

Steve seems to be eager to get things working as well as possible
so that we can use EVLA antennas during the calibrator flux survey
this weekend.  To accommodate this I prevailed upon Steve Myers to
steal the EVLA antennas and antenna 20 from him during the polcal
run this afternoon to try to get the antennas all up to snuff.

Much had been done to 14 and 16 over the last two days, both 
intentionally and unintentionally, so there was much to sort out.

Summary, more details lie below.
14B has an unknown problem; it fringes only weakly.
C band noise power to the T304s seems much too weak in 14.
In antenna 16, C band and X band noise power to the DTS needs 
to be much stronger than we would like to get enough power to 
the T4s.


Antenna 13
Seems fine.  It works at L and X band only with IFs A and C.
Delay and pointing should be good enough, and downconverter
attenuators are well set.


Antenna 14
something bad happened to it earlier today and Jerry spent much
of the afternoon getting it all together again.  Suffice it to 
say that it is more or less back to normal again; he can tell the
full story if he wants.

Once the antenna returned to service it was found that IF B
(only) had a delay error of about 15 ns.  This was fixed for 
X band, but no other for lack of time.  However the response
at all bands is very low and delays are not the only problem.
Perhaps the DTS module or deformatter would like to be reset,
but I did not try that.

C band is not there.  There is a rumour that the receiver is warm
but that is not consistent with the behavior.  To get enough power
into the sampler requires that both attenuators be set to zero.
This is true for all IFs.


Antenna 16
Seems to work, but there are peculiarities at C and X band.
To get enough power out of the deformatters for the T4 requires
driving the DTS modules very hard.  Only when the sampler value
RMS is between 30 and 60 is there enough drive to the T4 to allow
the ALC to level.  This happens for all IFs and only at C and X band.
The antenna does seem to fringe at C and X band, howver I can say
nothing about sensitivity.


General
At different times during this work both 14A and 16A disappeared.
I was able, after a while, to get them back again be reloading the
FIR coefficinets in the deformatter module.  Later Kerry admitted
to reloading FPGAs in some deformatters, so this event may not be
as spontaneous as it seems.