[evlatests] X-Band Tsys for new EVLA receiver

[Rick Perley]

    The first wide-band X-band receiver is now deployed on antenna 7.  
Gordon Coutts and I went out to the site this morning to do basic 
hot/cold measurements, from which the system temperature is derived. 

    As usual for these lower-frequency system, there is a small degree 
of uncertainty because we don't have a calibrated cold load, (the horn 
is too large), and must assume a sky emission and ground spillover 
contribution. 

    Gordon made FE wide-band measurements using a spectrum analyzer.  I 
used the bandpass tool to determine power spectra.  From the latter, and 
assuming the total spillover + atmosphere + CMB emission is 12K, the 
basic system parameters over the frequency range 7.8 to 8.8 GHz are 
given below:

Freq       Tsys        Tcal         Trcvr
---------------------------------------------
7.8 GHz  32           1.41           20
8.0          30            1.58          18
8.2          30            1.62          18
8.4          29            1.51          17
8.6          29            1.67          17
8.8          28            1.58          16
-----------------------------------------------

Gordon's FE measurements, using a spectrum analyzer, and assuming the 
same spillover, provided identical results over this frequency range.   
His measurements go out to 12 GHz -- he'll send around a note on these 
full band results later. 

Efficiency and elevation dependencies will be determined at a later time.