[evlatests] WIDAR P-band status update: 11AUG2014

[Huib Intema (NRAO)]

Dear testers

Here are the outcomes of a short VLA WIDAR P-band status test (few 
minutes on 3C48) we ran this morning. EA08, 11 and 13 were out, and EA20 
had no data. Major points of attention are:

+ EA06 LCP no longer has lower power (thanks for the fix!)
- EA18 now has a bandpass ripple on both polarizations (was OK before)
- EA17 still has high polarization leakage (17%)

-- Huib


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I've used the same analysis approach as previously, therefore can be 
interpreted in the same way. Antennas EA08, EA11 and EA13 were not in 
the array, and EA20 was not active. The following polarization labeling 
convention applies: RCP = horizontal dipole(s), LCP = vertical dipole(s).

* Swapped polarizations:
None!

* Antenna power levels (determined from gain calibration):
All antennas have similar (healthy) power levels, within ~30 percent of 
the 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. Larger ripples are seen on some 
antennas/polarizations. For each of these, the relative ripple peak-peak 
amplitude (A >= 0.20), the frequency width (F) and the associated cable 
length (L) are estimated:
- 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
- EA18 RCP: A = 0.25, F = 3.0 MHz, L = 50.0 m
- EA18 LCP: A = 0.25, F = 3.0 MHz, L = 50.0 m
Note that EA20 was not active; EA20 LCP had the worst bandpass ripple to 
date

* Polarization leakage (determined from a single, RFI-free 16 MHz subband):
After applying flux- and bandpass calibration, all antennas show a 
non-zero amplitude in the crosshand correlations RL and LR. Averaged in 
time and frequency, most antennas have a 0.05-0.10 amplitude signal 
(5-10 percent) in RL and LR relative to RR and LL (here, the median 
amplitude was calculated from the antenna to all other antennas). The 
following antennas have crosshand signals above 0.12:
- EA17 = 0.17