[evlatests] L-Band Performance

[Rick Perley]

In addition to the all-bands tests run yesterday evening, I ran a sweep 
of L-band, to check if (1) the characteristics noted earlier on L-band 
sensitivity still applied, and (2) to see if there were any notable 
changes in antenna 14, which has the wide-band OMT installed.

   The short answers are:

    1) Yes
    2) No

    Some details:

    Data were taken in spectral line, 16 channels in each of four 
parallel-hand correlations, with 12.5 MHz BW.  (This is done to 
calibrate around the phase buttonhook problem). 
    AIPS weights were used to judge sensitivity.  The source observed 
was 3C48.  Two 2-minute scans were taken at each of 7 frequency 
settings, giving 14 different frequencies from 1275 to 1740 MHz.  The 
elevation was high -- 65 degrees, for which the VLA antennas see no 
ground radiation, and are thus expected to perform better than EVLA 
antennas. 

    At low frequencies -- below 1350 MHz,  the EVLA antennas are 
generally competitive with VLA antennas in sensitivity.  Antennas 18 and 
24 are notably decent.  But antenna 14 is at or near the bottom of the 
sensitivity distribution. 
    At high frequencies, (above 1400 MHz in general, but especially 
above 1600 MHz), the EVLA antennas are all at the bottom of the 
sensitivity distribution, tyically about 30% poorer in G/T than the 
median VLA antennas. 
    Antenna 14 is at the bottom at every frequency.   I don't think this 
is due to the OMT -- it was in this position in most previous tests of 
this type. 
   
    On a bright note, all EVLA antennas tune very nicely at 1760 MHz, 
with good sensitivity, while virtually no VLA antennas get useable data.