[evlatests] WIDAR P-band status update: 28JUL2014

[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. I have condensed the output a bit. 
Major points of attention are:


+ EA12 and EA16 no longer have swapped polarizations

+ EA16 LCP is now alive and working fine


- EA06 LCP has lower power

- EA17 has increased polarization leakage
- EA20 LCP has a large standing wave issue



Thanks to Paul, Jerry and Mert for repairing EA12 and EA16!


-- Huib




---


I've used the same analysis approach as previously, therefore can be 
interpreted in the same way. Antenna EA13 was not in the array, and EA14 
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. Taking the median of these power levels as the reference, I 
found the following deviations:

- EA06 LCP = 0.36



* 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:

- EA08 LCP: A = 0.30, F = 19 MHz, L = 7.9 m
- EA20 LCP: A = 0.45, F = 16.2 MHz, L = 9.3 m

- EA21 LCP: A = 0.20, F = 6.2 MHz, L = 48.0 m

EA20 LCP ripple is by far the most serious. EA08 LCP went unnoticed 
until now.



* 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:

- EA04 = 0.13
- EA17 = 0.17


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