[evlatests] L-Band Tuning and Sensitivity

[Rick Perley]

There was two hours of available 'dynamic' time Friday evening, and 
noting that we have 8 EVLA antennas outfitted at L-band, I thought it 
would be a good use of time to test their tuning ranges and sensitivities. 

The antennas were tuned to frequencies between 1200 and 2000 MHz, in 
mode '4', with BW = 12.5 MHz.  The AC side stepped at multiples of 25 
MHz, starting at 1200 and ending at 1975 MHz.  The BD side started at 
1212.5, and ended at 1987.5 MHz, also in steps of 25 MHz.  At each 
frequency pair, we observed the calibrator 3C147 and nearby blank field.

This was a spectacular success.  All eight antennas tuned to all 
frequencies (with a few exceptions, noted below),
with excellent sensitivity (also with some exceptions, noted below).  
Most notably, the  entire new frequency range of 1720 to 2000 MHz is 
both tunable, and apparently free of RFI. 

A few caveats must be noted here:

Antenna 17 A and B (i.e., RCP) was dead -- as has been noted in earlier 
reports.  Something is not connected, it seems.
Antenna 26 A and C was dead -- this is a known result of the phase 
stability tests done last week.
Antennas 24 and 26 were late getting into the array, so in fact we were 
unable to determine their low frequency tunability and sensitivities.  
But there is no reason whatever to think them worse than the others. 

Antenna 13's sensitvity declines continuously from low to high 
frequencies, so much that it only nominally fringes above 1700 MHz.  We 
think we understand the origin of this. 
Antenna 14 is less sensitive overall than the others. 

The EVLA antennas, as a group, are more sensitive below 1400 MHz than 
the VLA, and about equally less sensitive than the VLA between 1500 and 
1700 MHz.  The differences are not great. 

Frequencies between 1537 and 1637 could not be tested well, due to RFI.  
All other frequencies within the tested range appeared free of strong RFI! 

A more detailed report will follow later.