VLA Test/Observation Coordination Meeting
                           B.G. Clark
                         April 21, 2005

1,  EVLA 

R. Perley reports that he has begun total power measurements on antenna
14 at Kband.  Measurements are in an early stage yet.  He has problems.  
The cal and system temperature measured on the antenna (using a hot load) 
are different from those measured in the lab.  In the lab, the cal temperature 
was 2.21 K and the receiver temperature was 17 K.  On the antenna, he measures 
3.1 K and 27 K, respectively.  The tipping curves are linear in sec z to about 
15d elevation, and then turn over.   This does not conform to expectations,
and is hypothesized to be due to extra spillover hitting the ground around
the edge of the subreflector at antenna elevations of about 20d.  More 
measurements will be made to clarify the situation.

B, Clark reports that difficulties with a digitizer module redesign will 
delay the first astronomical tests of the redesigned module to May if not
June.

K. Sowinski has conducted on-sky measurements of the block frequency converter
which will be used in the new 15 GHz, 25 GHz, 35 GHz and 43 GHz receivers.
It is considered important to verify performance of the device so that a 
large order can be placed to equip the entire array.  The block converter 
will have two paths, one, the direct path, simply passes a 4 GHz bandwidth
directly to the downconverters.  A second path converts the second 4 GHz
band down to the range that can be handled by the downconverters.  A preliminary
measurement, made at K band, indicates that this second path is losing 
signal-to-noise, perhaps by a factor of two, relative to the first path.

K. Sowinski reports on pointing measurements made with antenna 14.  The
azimuth errors he sees are comparable with other antennas, but he sees 
larger scatter in elevation.  If he permits the parameter solving program
to solve for tilt of the azimuth axis separately from azimuth and from
elevations pointing error, he gets different numbers, a symptom of something
systematically wrong with the pointing equation - an unmodeled, or incorrectly
modeled effect.

2.  196 MHz system.

C. Carilli reports that they have moved to 230 MHz, with a 12 MHz bandwidth,
for the moment, to avoid interference.  This despite the fact that the 
science they want to do is at 196 MHz.  At 230 MHz they can observe, at 
least on the stronger sources, but calibration uncertainties remain, and 
they don't know, really, what system temperature and efficiencies they 
are obtaining.

At 196 MHz, even in the presence of the interference, they can detect
fringes on Virgo A, though weaker sources would be problematic.  They
are looking into the possibility of having the digital television station
on channel 9 turned off, to make sure there is no other major interferer
lurking just below.