[evlatests] P-Band Ready for Prime Time!

[Rick Perley]

    I've done a complete and careful survey of P-band capabilities on 
EVLA antennas 14, 17, and 23.  The latter two have the new 4/P 
converters, and are the prototypes for the rest of the array. 

    Summary:

    Everything looks normal.  In fact, it looks better than normal:  The 
10 and 12.5 MHz internal birdies that we have had to live with for so 
very long are completely absent from the EVLA antennas (as they should 
be!)  And I can see no unexpected birdies -- even in total power -- to 
replace these.   The spectrum is 'clean as a whistle'. 

    Details:

    I tuned from 295 to 340 MHz, in 5 MHz steps, with 6 MHz BW, in mode 
'4', and observed 3C48, a well known calibrator.  Bandpasses were 
derived, gains calibrated, and weights determined, using oft-described 
standard methods.  Due to a late start, the EVLA missed the 300/305 MHz 
tuning.  (But they worked for the 295 MHz tuning, so we can safely 
extrapolate). 

    Results:

    1) Birdies are present on VLA antennas at all multiples of 10 MHz.  
Especially strong is 300 MHz. 
    2) None of these birdies are present on the three EVLA antennas. 
    3) Weak birdies are seen at 312.5 MHz on the VLA, which are absent 
on EVLA.
    4) RFI was seen on all antennas at 304.5 MHz (origin unknown to me), 
and 332.8 MHz -- this one is the well known RFI from the ABQ airport.   
These are not strong, and of no major concern. 
    5) Bandpass shapes for EVLA look as expected (meaning, the 
amplitudes are similar to VLA, and the phase has the famous 'hook' at 
the low frequency end). 
    6) Phase and amplitude stability -- within the 5-minute scan lengths 
I used -- are great, EXCEPT for 14C, which has some really interesting 
problems.  See below for a description. 
    7) Sensitivity, as judged by AIPS weights, are all within reasonable 
bounds.  There is a significant spread, whose origin is unclear to me.  
The spread is by about a factor of 2 in weights -- roughly a 40% maximum 
variation in G/T.  What is interesting is that antenna 14 is 
*consistently* the best in the entire array in sensitivity.  Antennas 17 
and 23 are both better than the VLA average, at all frequencies.  
Overall sensitivity drops dramatically below 305 MHz (no surprise!), and 
is heading down at 340 MHz.  I didn't try 345 MHz. 

    I advocate going ahead full steam on outfitting the rest of the array.