[evlatests] EVLA Sensitivity, from 1 to 12 GHz

[Rick Perley]

    The 'receiver rotation trick' test allows us to get an honest 
estimate of our true array sensitivity.  I'm observing 3C147 -- a strong 
source of know flux density, and some blank sky nearby. 

    The data from last night has been calibrated.  (There is an 
interesting problem in that the 3C147 models are slightly wrong for this 
configuration, and caused a miscalibration of the long spacings by a few 
percent ...  This is an argument for getting better models soon). 
   
    Noise histograms were made for all subbands that I observed (a total 
of 96!), using only channels apparently free of RFI, and antennas that 
are fully EVLA compliant.  These histograms were converted to SEFD, with 
some of the results given below. 

    L-Band:

    The lowest 4 subbands (982 through 1244 MHz) are greatly affected by 
RFI.  The histograms were strikingly non-gaussian, so the results are 
not meaningful until we understand the origin.  Certainly a higher 
spectral resolution is needed (I used 1 MHz).  Emmanuel will soon be 
doing this. 
    Freq         SEFD
------------------------
    1270          633
    1350          483
    1400          450
    1470          454
    1510          478
    1600          553
    1660          551
    1720          572
    1790          502
    1850         415
     1920        415
     1970        553
--------------------

    S-Band

Like C-band, the sensitivity in the lower half (2 -- 3 GHz) is worse 
than the upper half (3 -- 4).
  SEFDs are near 400 from 2.05 through 2780 MHz, then drop to 340 at 
3160 MHz, and to 300 Jy at 3540 MHz, rising a bit to 340 Jy by 3800 MHz. 

    C-Band

SEFDs decline from ~350 Jy at the low frequency end (4.1 GHz) to about 
290 Jy through to 6 GHz, above which it drops to 230 -- 250 Jy right up 
to 8 GHz. 

    X-Band

 We have now 5 new-style receivers in, allowing full band sensitivity 
measurements for the first time.  The results are good. 

    SEFDs are remarkably uniform throughout the entire band:  between 
235 and 260 Jy, except at the extreme ends.  If we assume the efficiency 
is 60%, this sensitivity corresponds to an average Tsys of about 26K. 

    A more report will follow when the rest of the data are in.