[evlatests] P-band status update

[Huib Intema (NRAO)]

Dear testers,


Here are the outcomes of a short P-band status test (few minutes on
3C147) we ran last Wednesday evening. Antennas EA14 and EA21 were out of the
array, while antenna EA17 was dead. The following polarization labeling
convention applies: RCP = horizontal dipole(s), LCP = vertical dipole(s)


* Antenna power levels (determined from gain calibration):

Most antennas have similar (healthy) power levels, within a factor of
two of their median. Taking the median of these power levels as the
reference, I noticed a few low outlier antenna/polarization pairs with
the following relative power levels:
- EA04: LCP = 0.19
- EA05: RCP = 0.08, LCP = 0.22
- EA16: RCP = 0.02

Similarly, the following antenna/polarization pairs have marginally low
relative power levels:
- EA06: LCP = 0.50
- EA13: RCP = 0.45, LCP = 0.46
- EA18: LCP = 0.44


* 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. The following antenna/polarization pairs show
clear evidence of ripples in amplitude and/or phase across frequency,
indicating standing wave issues; for each the relative ripple peak-peak
amplitude (A), the frequency width (F) and the associated cable length
(L) are estimated:
- EA16 RCP: A = 1.0, F = 87.5 MHz, L = 1.71 m
- EA20 RCP: A = 0.65, F = 20.0 MHz, L = 7.5 m

Similarly, the following antenna/polarization pairs have smaller ripples:
- 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 RCP: A = 0.10, F = 3.4 MHz, L = 43.5 m
- EA10 LCP: A = 0.20, F = 3.3 MHz, L = 45.0 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


* 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 antenna has significantly higher crosshand signals:
- EA22: 0.26 in RL, 0.27 in LR

Similarly, there was one antenna with a higher signal in just one
crosshand:
- EA18: 0.15 in RL, 0.06 in LR



-- Huib