[evlatests] EVLA Performance, Nov 28

[Rick Perley]

    I ran a system check, for all antennas and bands, last night, with 
the standard setup:

    - Spectral Line mode '4', 12.5 MHz BW, giving 16 channels in each of 
the four correlations.
    - Default frequencies (except at L-band, where I put the AC side to 
1485 MHz, to avoid the 'suckouts')
    - 5 second averaging.
    - Observed a strong point-source for two scans of two minutes at 
each band. 
    - Referenced pointing was done at all bands, except L-band, to try 
ensure on-axis gains. 

    In general, the EVLA antennas performed very well indeed!  
Viritually no flagging was needed (other than antennas without 
receivers), and not funny data (defined as jumps in amplitude or phase) 
were seen *within any one scan*. 

    However, the now-familiar system-wide phase jump was noted at every 
band, between the two observations made at each band. 

    Band-dependent details follow:

    1) L-band

    All EVLA antennas performed nicely, except 23. 
    There was a global phase jump of 84 degrees (at 1485 MHz) and 50 
degrees (at 1385 Mhz) (plus/minus a couple of degrees) between the two 
observations, made 21 minutes apart. 
    Sensitivity of antennas 13, 14, 16, and 26 are below the VLA 
average.  Sensitivity of 18 and 24 are near the VLA mean. 

    2) C-Band

    Antennas 23 and 26 were both dead on all IFs. 
    A global phase jump of about 110 degrees (both AC and BD ) occured 
between scans.   There is evidence the jumps are of different size for 
some antennas:  120 degrees (AC) and 95 degrees for 14, 16, and 24, but 
104 (AC) and 110 (BD)for antennas 13 and 18.  See below for better 
evidence at other bands ...
    The 5 working antennas remain the most sensitive in the array.  
Antenna 13 is the poorest of the EVLA antennas -- about the same as the 
better VLA antennas. 
    The pointing corrections determined were very large for some 
antennas:  0.4 arcminutes in El for antenna 14, 0.7 arcminutes in Az for 
antenna 24. 

    3) X-Band

    Antenna 23 gave no useable data.  All others performed well. 
    A global phase jump -- with different values for different antennas, 
was noted:  Antennas 14, 16, 24 and 26 jumped by 90 degrees on AC, and 
by 140 degrees on BD, while 13 and 18 jumped by 55 degrees on AC, and 
110 on BD. 
    Antennas 13, 16, 18, 24 and 26 have normal sensitivity.  Antenna 14 
is rather poorer on the AB side, and very poor (sensitivity down by a 
factor of about 2) on the CD side. 
    pointing corrections were not as extreme at X-band as at C-band, but 
still notable:  0.3 arcminutes in El for antenna 14, and 0.3 arcminutes 
in Az for antenna 24. 

    4) K-Band

    Antenna 23 gave no fringes, and antenna 26's K-band fringes are so 
weak as to be barely discernible. 
    There was again a global phase jump -- of two different magnitudes 
for different antennas:  Antennas 13 and 18 jumped by 100 and 135 
degrees (AC and BD), while the others jumped by 150 and 85 degrees (AC 
and BD). 
    Referenced pointing failed for antenna 26 -- possibly because of the 
low sensitivity, but also possibly due to a large pointing error.   The 
solutions obtained (all differential w.r.t X-band) are small, except for 
antenna 24, for which the El collimation was -0.3 arcminutes.
    Sensitivities for antennas 13, 14, 16, and 18, are all about 
normal.  Atnenna 24's sensitivity is about a factor of 2 to 4 too low.  
Antenna 26's sensitivity is at least an order of magnitude too low. 

    5) Q-Band

    No fringes from 23 or 26 -- all others fringed well. 
    The `global' jumps are more difficult to discern, as the phase 
stability is of nearly similar magnitude.  There was certainly a jump 
between scans, with a magnitude of near 100 degrees.  A more careful 
perusal will be needed (to follow).
    Referenced pointing worked for 13, 14, 16, 18, and 24.  Differential 
(collimation) corrections were small (0.1 arcmin) for all antennas. 
    Sensitivities of all 5 antennas are within normal bounds.  It should 
be noted that antenna 24 is easily the best in the array.