[evlatests] WIDAR P-band status update: 28/30AUG2014

[Paul Harden]

On 9/2/2014 11:57 AM, Huib Intema (NRAO) wrote:
> Dear P-banders,
>
> Here is the combined outcome of two short VLA WIDAR P-band status tests
> (few minutes on 3C286 and 3C48) we ran on Aug. 28 and 30. EA11 was out.
> Major points of attention are:
>
> + EA17 now has normal polarization leakage (thanks for the fix!)
> - EA17 has swapped polarizations

Will swap the dipole feeds shortly.

> - EA18 LCP has a very low gain

We'll check this as well.

> - EA08 LCP, EA20 LCP, and EA23 RCP have very large bandpass ripples

The apex cable at EA23 will be repaired this week to reduce the ripple 
to support VLITE.  We'll check EA08 and 20 as well.  EA23 has priority.

> * Polarization leakage (determined from a single, RFI-free 16 MHz subband):
> Most antennas show a non-zero (0.05-0.10, or 5-10 percent) amplitude in
> the crosshand correlations RL and LR, except:
> - EA19: A = 0.13

Dipoles are mounted in the antenna to a slip-ring type assembly in the 
barrel to keep the dipole fixed but allow the subreflector to move. 
There is some inherent "slop" when the dipole is bolted in place, 
allowing a few degrees of "wiggle."  This slop no doubt changes a bit 
over time due to antenna vibration and elevation angle.  I think 5-10 
percent is probably the amount of "background" cross-polarization 
leakage to be expected due to the mechanical slop of the dipole mounting.

We'll look at EA19 for an excessive offset in alignment or other cause.

Paul