[evlatests] L-Band Pointing

[Ken Sowinski]

On Wed, 24 Jan 2007, Rick Perley wrote:

>    Most *VLA* antennas show a significant offset in elevation pointing
> -- perhaps as large as an arcminute.  Notable ones are:  1, 2, 3, 4,  8,
> 15, 19, and 28.  No VLA antenna is as good as the EVLA antennas (except
> 17).  Clearly, the good behavior of the EVLA antennas is a result of the
> collimation corrections put in by Ken last week.  But why are the VLA
> antennas mispointing at L-band so badly?

I think it is squint.

VLA antennas have an offset of about an arc minute in both
Az and EL between RCP and LCP.

The EVLA L band horns or on the downside of the feed circle
and almost all the squint is in Az.

You looked at amplitude traces in only one polarization; should
you choose the other the apparant pointing offset will change sign
if this is really the reason.