[evlatests] Feb 7, 2006

[Ken Sowinski]

                        EVLA Tests, February 7, 2006

Many interesting things were seen, only a little was learned,
and P band was attempted.  I will list things in more or
less chronological order.

Barry, Bryan and I have been discussing funny commands to 
ACUs when an executor is started.  This happened when I began 
today but only for antenna 13, not 14 nor 16.

The 14A and 14D deformatters had to have their FIR coefficients
reloaded.  This was true yesterday as well but Michael did not 
see this because he never got antenna 14.  

Antenna 16 seemed to be coming and going, but settled down about
the time I settled down to try to find out what it was doing.
I suspected the ACU, but see what happened later in the day as
described below.

Proceeding through the bands I found the L301-1 in antenna 16 was
not working.  This broke AC at L and C, and all IFs at K and Q.
It took a power reset to get it going again.  This was likely
broken yesterday as well as it is consistent with all the lack
of fringes that Michael reported.

An attempt was made at P band.  Rob reported to me later that it
is conceviable that the receiver was off at the time, so take
all this cum granus salis.  
1.  The samplers were being driven very hard; it took lots of
attenuation to get the sampler RMS down to the 10 or so that
we usually use.  It is not even clear that this is the best value
for P band.  Regardless of attenuator settings there was no or
little power seen in the T5.  final attenuator settings:
IF  RF   OUT
--  --   ---
A   30   18
B   30   27
C   30   23
D   30   22

2.  To get reasonable power in the T5 the deformatter gain had
to be around 120, four times larger than the nominal 30 we use
now.  I would suppose that this is necessary to compensate for
the narrower P band signal, but Rick assures me that the receiver
has a 50 MHz bandpass filter so maybe the receiver was turned off.
Once TP levels were reasonable no sync detector signal was seen.
Has it been turned on for P band?

3.  The VLA was setup to 325.9375 and 320.0 MHz at AC and BD.
The synthesizers were not all tuned according to Barry's tuning
plan.
        Actual       Expected
        ------       --------
L301-1  12160        12160
L301-2  12160        12160
L302-1  13690.2625   13690.0625
L302-2  13696.0000   13679.9000

The difference in L302-1 could be a computational error in the 
tuning plan, the second is just weird.  

No fringes were seen.  A bandpass was seen in autocorrelation with
a very large spur at about 327 MHz.  If anyone wants to look at the 
data I can provide a time range for P band data, or, just help yourself 
and look around.


After finishing with P band the system seemed to be in great disarray.
The correlator was upset and had to be reset.  Even after that EVLA
antennas were very unstable, going up and down every minute or so.
All three antennas did it at the same time; even EVLA only baselines
showed the problem.  Phases went to pot when it happened, but returned
to the same place when the episode finished.  The three antennas did
not all seem to be affected to the same degree; antenna 16 was by far
the worst.  I discussed this with Rob and Jim who were out there and
as we started looking into it the system stablilzed again.  It has all
the earmarks of phase switching problems.  Can it be that something
is making the heartbeat wander in all the antennas at the same time?



The last hour and a half or so was given to Vivek for a sensitivity
survey and to look for the deformatter generated spurs that Mike has
been fighting.  I predict that 14D and 16B will not look too good.