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

[Dan Mertely]

Thanks for the review Huib.  Allen & I expect to be installing
another MJP (on ea10 at DE9) this week, but after that we'll take a
look at ea06 & ea17.  ea17 might have a improperly-aligned P-band
cross-dipole.  ea06 has always shown poor SNR on the expected RFI.
I suspect a problem in the FE.  We'll check it out more thoroughly
soon.  We already know the cause of the ea20 L/X/V side ripple &
plan on replacing the cable or connector at a convenient moment.

-Mert

On 7/28/2014 2:48 PM, Huib Intema (NRAO) wrote:
> Hopefully the formatting is better now ...
>
> ---
>
> 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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