[evlatests] antenna 18 works

[Ken Sowinski]

>  The antenna appears to be 
> safe for movement (including over the top) and we have switched power at 
> X-band on IF's A and C.
> 
> Rob Long

The antenna worked as expected almost immediately.  There were
large delay and az offset errors to pin down, but no major problems.
Fringe tracking and phase switching both appear to work.  

This was the most trouble-free new EVLA antenna yet.

Despite the winds we are now doing pointing to make the antenna
more useful in the short term.  Later I will try to optimize focus.

The only obvious problem seen so far is that the backend SD voltages
are not as stable as we expect: there are variations of about five
percent on a time scale of seconds.