[evlatests] EVLA tests, Dec 22 2005

[Ken Sowinski]

                         December 22, 2005

Except for 16B at L band the EVLA antennas seemed to be working.
The DTS module in 16B does not seem to be happy with L band.
When all was settled down, the system was given to Rick to try
again the measurements that were not taken Tuesday night when
the antennas stopped pointing.  He will report in due time.

After that I had more careful look at level setting and hunted 
birdies.

Levels.
C band
14 BD are both broken.  With the traditional attenuator settings
large RMS are seen in the sampler statistics: ~70 in B and ~60 in D.
If attenuation is cranked in, to force the sampler statistics to
the usual 5-10, there is not nearly enough power to level the T4
modules.  This is not a systemic problem because it is not seen
at any other band.

X and Q band both looked normal.

K band
16B was exhibiting the same DTS pathology I saw on Tuesday.  It
was not doing it earlier today.  Adding 6 dB to the output attenuator
brought the sampler RMS from 20 (and sometimes 40) to a stable 10.

L band 
16B just doesn't work.  It is clear that there is something wrong in 
the DTS module which gets triggered when interference passes by.  Even
cranking in enough attenuation to reduce the sampler RMS to ~3.5
did not make the DTS instability go away, but there was still enough
signal to allow the T4 to level.  It seems there is something extra
in the signal presented to the T4.


Birdies
I thought it was time to see if the strong birdies that were 
seen in the past are really gone.  The remedy tried a while ago was
to crank up the deformatter output to drown the spur and then reduce
the signal with pads to the T4 input spec.  I don't really remember what 
pads are used on what signals, but perhaps someone can fill this in.
The only spurs seen were at around ~700 kc and look like what we have
in the past attributed to switching regulators on the deformatter cards.
The presence of birdies was checked only with 10 second integration.  
It is likely they would be seen on all IFs with enough integration.  
In 10 second integrations nothing was seen in 14B, 14D and 16B.  If
anyone really wants to look at the data I can reconstruct the times.

14A
This one was very strong and could be seen in autocorrelation even
in 25 MHz total BW (about 800 kc/channel).  In 3 MHz total BW it
could be seen in correlation with 16 and in autocorrelation in 16 as
well.  At 1.5 MHz total BW it could be seen on a baseline to a VLA
antenna: 9 x 14.

14C, 16D
These could be seen only when the BW was 6.25 MHz or narrower

16C
This one was visible only in 3 MHz total BW.