[evlatests] A curiosity with antenna 12

[Rick Perley]

    Michael took a short (27 minute) observation in 2 GHz-wide mode a 
couple days ago.   Eight full-polarization subbands, each of 128 MHz 
width, in each of the AC and BD IFs.  In general, beautiful data. 

    It was noted that antenna 12 had a curiousity -- once every minute, 
on all subbands, in all polarizations, the amplitude dropped by about 
10% for a single 1-second record.  This was the only antenna for which 
such a effect was noted.  As the script asked for a new scan every 
minute, I had assumed the 'drop-down' was a first-record, or perhaps 
second-record problem.  It's not!

    This 'drop-down' is a 2nd-record effect -- the 2nd record of every 
scan is low by this much.