[evlatests] X-Band Sensitivity -- Superb!!!

[Rick Perley]

    As part of the upcoming 'path to completion' review, I'm executing 
some tests to determine the EVLA's basic characteristics. 
    Last night, under ideal conditions, I did a 'sensitivity' test:  
Using old-style 'OSRO' mode (two subbands, 128 MHz width, 2 MHz channel 
resolution), tuned to reasonably placed frequencies in each of the eight 
bands.  I observed 3C147 to establish the amplitude scale, then to a 
blank field 2 degrees away to measure the noise.  Referenced pointing 
was applied.  The usual basic calibration was done. 

    Here I report only on x-band -- the others will follow as time 
allows today. 

    All antennas -- except ea05 -- which were in the array fringed as 
expected.  (antennas 19 and 20 are out). 

    From the naturally-weighted noise maps, we measure the SEFD directly 
using the map rms, using all working antennas. 

    8300 MHz:  SEFD = 270 Jy
    11300 MHz:  SEFD = 250 Jy. 

    We can get a good measure of the system temperatures and antenna 
efficiencies by using the switched power measures, after correction by 
the calibration from 3C147.  (The 'raw' Tsys values use the measured 
Tcal provided from engineering.  Any errors in these are measured by 
calibration against a source of known flux density, since the observed 
visibilities have been converted to Jy by the provided Tsys values). 

    Adjusting the measured Tsys values by the gain factors gives the 
average Tsys:  (these are eyeball averages -- but the spread is 
impressively small, so they should be pretty decent estimates). 

    8300 MHz:  Tsys ~ 28 K
    11300 MHz:  Tsys ~ 26K

    Finally, we can then measure the efficiencies by using the SEFD values:

    effic. = 5.62*Tsys/SEFD  (where 5.62 comes from the antenna's 
collecting area and Boltzmann's constant).

    8300 MHz:  Effic ~ 0.56
    8700 MHz:  Effic ~ 0.57

    I guesstimate the accuracy of these values as a few percent.  A 
better analysis will follow, in due time (but well before the 
presentations to our august visitors ...)

    Bottom line:  The sensitivity is considerable better than the 
Project Book specifications (SEFD = 340 Jy at 10 GHz).   As the 
efficiencies are exactly what we expect (and they should be!!!), it's 
the outstanding receivers which are allowing us to boast (just a bit!). 

    Congratulations to all!