[evlatests] WIDAR P-band status update: 13SEP2014

[Huib Intema (NRAO)]

Dear P-banders,

Here is the combined outcome of two short VLA WIDAR P-band status tests 
(few minutes on 3C48) we ran on Sept 5 and 13. EA26 was out in both. 
Major points of attention are:

+ EA20 no longer shows the huge bandpass ripple on LCP (thanks for the fix!)

~ EA23 no longer shows the large bandpass ripple on RCP
   Was this fixed or is this intermittent?

- EA04 has very low gain in RCP, and low gain in LCP
- EA08 has large bandpass ripple in LCP
- EA11 has either loose / rotated feed, or swapped polarizations + huge 
polarization leakage
- EA13 has large bandpass ripple in LCP
- EA14 has low gain in RCP
- EA16 has low gain and erratic bandpass in RCP (Sept 13 only)
- EA17 has swapped polarizations and low gain in LCP (after software swap)
- EA18 has low gain in RCP
- EA19 has low gain in RCP
- EA28 has fast bandpass ripple on LCP

-- Huib



I've used the same analysis approach as previously, therefore can be 
interpreted in the same way. Antenna EA26 was not in the array. The 
following polarization labeling convention applies: RCP = horizontal 
dipole(s), LCP = vertical dipole(s).

* Swapped polarizations:
- EA11 (or possibly a rotated feed)
- EA17 (after the dipole fix)

* Antenna power levels (determined from gain calibration):
Most antennas have similar (healthy) power levels, within ~30 percent of 
the median, except:
- EA04 RCP: P = 0.05
- EA04 LCP: P = 0.40
- EA14 RCP: P = 0.35
- EA16 RCP: P = 0.35
- EA18 RCP: P = 0.45
- EA19 RCP: P = 0.45
(P = power level relative to median)

* Bandpass ripples (determined from bandpass calibration):
Most antennas have (healthy) smooth bandpass amplitude structure and 
linear phase structure across frequency (224-480 MHz; ignoring the 
ranges with known RFI), except:
- EA02 RCP: A = 0.15, F = 5.9 MHz, L = 25.5 m
- EA02 LCP: A = 0.15, F = 6.2 MHz, L = 24.0 m
- EA08 LCP: A = 0.30, F = 17. MHz, L = 8.7 m
- EA13 LCP: A = 0.35, F = 20. MHz, L = 7.5 m
- EA14 RCP: possible large ripple, F ~ 75. MHz, L = 2.0 m
- EA16 RCP: erratic bandpass
- EA17 LCP: upturn in upper 1/4th of the band
- EA28 LCP: A = 0.25, F = 3.6 MHz, L = 42.0 m
(A = relative ripple peak-peak amplitude, F = the ripple frequency width 
, L = associated cable length)

* Polarization leakage (determined from a single, RFI-free 16 MHz subband):
Most antennas show a non-zero (0.10-0.15, or 10-15 percent) amplitude in 
the crosshand correlations RL and LR, except:
- EA11: A = 0.42(!)
(A = polarization leakage, relative to the parallel hand signal)



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