[evlatests] WIDAR P-band status update: 28/30AUG2014

[Huib Intema (NRAO)]

Dear P-banders,

Here is the combined outcome of two short VLA WIDAR P-band status tests 
(few minutes on 3C286 and 3C48) we ran on Aug. 28 and 30. EA11 was out. 
Major points of attention are:

+ EA17 now has normal polarization leakage (thanks for the fix!)
+ EA18 no longer shows the fast bandpass ripple
- EA17 has swapped polarizations
- EA18 LCP has a very low gain
- EA08 LCP, EA20 LCP, and EA23 RCP have very large bandpass ripples

-- Huib


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I've used the same analysis approach as previously, therefore can be 
interpreted in the same way. Antenna EA11 was not in the array. The 
following polarization labeling convention applies: RCP = horizontal 
dipole(s), LCP = vertical dipole(s).

* Swapped polarizations:
- 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:
- EA18 LCP: P = 0.05 (after MJP install)
- EA20 LCP: P = 2.15 (related to bandpass ripple, see below)
- EA23 RCP: P = 0.63 (related to bandpass ripple, see below)
(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 = 0.85, F = 16.6 MHz, L = 9.0 m (may have gotten worse)
- EA20 LCP: A = 0.80, F = 16.6 MHz, L = 9.0 m (may have gotten worse too)
- EA23 RCP: A = 0.60, F = 20 MHz, L = 7.5 m
- 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 (0.05-0.10, or 5-10 percent) amplitude in 
the crosshand correlations RL and LR, except:
- EA19: A = 0.13
(A = polarization leakage, relative to the parallel hand signal)