[evlatests] WIDAR P-band status update: 28JUL2014
Huib Intema (NRAO)
hintema at nrao.edu
Mon Jul 28 16:48:12 EDT 2014
Hopefully the formatting is better now ...
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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
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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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