[evlatests] P-band status update: 02MAY2014

Tue May 6 15:10:38 EDT 2014

Dear testers,

Here are the (somewhat delayed) outcomes of a short VLA P-band status 
test (few minutes on 3C147) we ran last Friday around noon. I've used 
the same analysis approach as previously (26MAR2014 and 15APR2014), 
therefore can be interpreted in the same way. Antenna EA12 was out of 
the array. The following polarization labeling convention applies: RCP = 
horizontal dipole(s), LCP = vertical dipole(s).

Generally, I found the antenna status to be mostly the same as the 
previous status update (15APR2014). EA14 RCP was dead (which is a known 
problem). Positive differences that I noticed are:
- EA04 cross-polarization now below 0.1
- EA28 cross-polarization now below 0.1

* Antenna power levels (determined from gain calibration):

All antennas have similar (healthy) power levels, within a factor of two 
of the median. Taking the median of these power levels as the reference, 
I noticed a few marginally low outlier antenna / polarization pairs with 
the following relative power levels:
- EA06: LCP = 0.47
- EA13: RCP = 0.55
- EA18: LCP = 0.30
- EA19: RCP = 0.56

Rick reported earlier today on low power on EA03, which was not (yet) 
seen in this test data.

* 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:
- EA20 RCP: A = 0.65, F = 20.0 MHz, L = 7.5 m
- EA20 LCP: A = 0.25, F = 16.7 MHz, L = 9.0 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
- 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
- EA14 LCP: A = 0.15, F = 20.0 MHz, L = 7.5 m
- EA21 LCP: A = 0.20, F = 6.2 MHz, L = 48.0 m
- EA28 LCP: A = 0.15, F = 3.8 MHz, L = 39.0 m

Rick reported a strong ripple on EA19 LCP, which is not (yet) seen in 
this test data.

* 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 marginally higher crosshand signals (above 0.10):
- EA17: 0.15 in RL, 0.16 in LR
- EA18: 0.13 in RL
- EA20: 0.12 in RL, 0.11 in LR

* Psum (inspected with AIPS SNPLT) For most antenna/polarization pairs, 
the time-series of Psum values as inspected for two individual RFI-clean 
subbbands (or IFs) lie closely around a constant value of about 15 
counts. I've noticed the following exceptions:
- EA19 RCP: Psum slopes down from 15 to 12 over 8 minutes
- EA19 LCP: Psum jumps from 15 to (noise around) zero after 6 minutes

* Pdif (inspected with AIPS SNPLT) For most antenna/polarization pairs, 
the time-series of Pdif values as inspected for two individual RFI-clean 
subbbands (IFs) lie closely around a constant value between 0.4 and 2.0 
counts. I've noticed the following exceptions:
- EA03 RCP: low value of 0.1
- EA03 RCP: low value of 0.3
- EA06 LCP: low value of 0.2
- EA13 RCP and LCP: noise around zero
- EA18 LCP: low value of 0.1
- EA19 RCP: slopes up from 0.2 to 0.3 over 8 minutes
- EA19 LCP: Pdif jumps from 0.4 to (noise around) zero after 6 minutes
- EA20 RCP: low value of 0.01
- EA27 LCP: more noisy (scattered) than other Pdif time series

-- Huib

On 15-Apr-14 22:59, Huib Intema (NRAO) wrote:
> Dear testers,
>
> Here are the outcomes of a short VLA P-band status test (few minutes 
> on 3C147) we ran today around noon. I've used the same analysis 
> approach as previously (26MAR2014; see e-mail included below), 
> therefore can be interpreted in the same way. Antenna EA14 was out of 
> the array, while antenna EA03 was dead. The following polarization 
> labeling convention applies: RCP = horizontal dipole(s), LCP = 
> vertical dipole(s).
>
> Improvements compared to the previous test:
> - EA04 LCP had low power, now 'normal'
> - EA05 RCP and LCP had low power, now 'normal'
> - EA16 RCP had low power, now 'normal'
> - EA07 LCP had bandpass ripple, now 'normal'
> - EA10 LCP had bandpass ripple, now 'normal'
> - EA16 RCP had bandpass ripple, now 'normal'
> - EA22 had high cross-polarization, now 'normal'
>
> These changes reflect the work that Paul, Mert, Greg and company have 
> put into fixing things (thanks!).
>
> -- Huib
>
>
> * Antenna power levels (determined from gain calibration):
>
> All antennas have similar (healthy) power levels, within a factor of 
> two of the median. Taking the median of these power levels as the 
> reference, I noticed a few marginally low outlier antenna / 
> polarization pairs with the following relative power levels:
> - EA06: LCP = 0.51
> - EA13: RCP = 0.55
> - EA19: RCP = 0.46
>
>
> * 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:
> - 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
> - 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
> - EA28 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 antennas have marginally higher crosshand signals (above 0.10):
> - EA04: 0.12 in RL, 0.12 in LR
> - EA17: 0.14 in RL, 0.13 in LR
> - EA20: 0.13 in RL, 0.12 in LR
> - EA26: 0.13 in RL, 0.12 in LR
> - EA28: 0.13 in RL, 0.13 in LR
>
>