[evlatests] L-Band Sensitivity

[Rick Perley]

    From the AIPS Weights, for the 8 working EVLA antennas, we derive 
rough estimates of the sensitivities.  The antenna elevation declined 
from 80 to 40 degrees during the test, so I give these rankings at these 
extrema.

IFs A and C: (1465 MHz):

El = 80:  Antennas 18, 23, and 24 are typical of VLA antennas.  13, 14, 
16 and 17 (and antenna 17A much worse) than any other VLA antenna.  
(Antenna 26 was dead for these two IFs) . 

El = 40:  Antennas 18, 23 and 24 are better than all other VLA 
antennas.  The others remain worse than all VLA antennas. 

IF B and D:   (1385 MHz):

El = 80:  Antenna 18, 23 and 24 are again typical of median VLA 
antennas.  13 and 16 are typical of the poorer VLA antennas.  14 and 26 
are worse than any VLA antenna.  (17B was removed due to the square-wave 
phase pattern messing the calibration,  but 17D is about the same as 14 
-- quite poor compared to VLA antennas). 

El = 40:  The 'golden trio' (18, 23 and 24) are much better than any VLA 
antenna.  The other 5 are typical of median VLA antennas. 

************************


These results are consistent with the results from the single-antenna 
tests done by Bob and me last month on antennas 14 and 24:

a) The EVLA efficiency is lower than the VLA's -- typically 43% compared 
to 50%.
b) The EVLA efficiency has a notable variation with frequency:  a maxima 
near 1250 and 1850 MHz, and a minimum midway between.  (typically 45% at 
peak, 39% at minimum).
c) Antenna 24 has extraordinarily good system temperature (about 25K)
d) Antenna 14 has very poor system temperature (about 35K), a good 
portion of which seems to arise after the first stage of amplification. 
e) The EVLA antennas have a very much flatter system temperature 
variation with elevation than the VLA antennas.