[evlatests] P-band status update: 24JUL2014

[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. Major points of attention are:

- EA12 and EA16 have swapped polarizations
- EA16 LCP is (almost?) dead
- EA20 LCP has a large standing wave issue

---

I've used the same analysis approach as previously, therefore can be interpreted in the same way. Antennas EA13 and EA28 were not in the array, and EA14 was taken for maintenance. The following polarization labeling convention applies: RCP = horizontal dipole(s), LCP = vertical dipole(s).


* Swapped polarizations:
- EA12
- EA16
Note that for EA12, one of the few antennas mounted with a permanent 4-band feed, it was also found that the 4-band polarizations are swapped. For the rest of this report, I have manually corrected the data for these swapped polarizations.


* 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 = 0.46
- EA10 LCP = 4.35
- EA16 LCP = 0.01
- EA19 RCP = 0.62
So EA16 LCP has very low signal. EA10 LCP has high power, but otherwise looks OK


* 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), 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
- EA11 RCP: A = 0.15, F = 3.3 MHz, L = 45.0 m
- EA11 LCP: A = 0.15, F = 3.8 MHz, L = 39.0 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.


* 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 0.10:
- EA04 = 0.13
- EA17 = 0.15
- EA19 = 0.13
- EA26 = 0.13


-- Huib



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