[evlatests] A curiosity with antenna 12

[Ken Sowinski]

On Fri, 25 Jun 2010, Rick Perley wrote:

>    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.

this is still happening.  It is really synchronous with the
the new scan and is happening at the antenna.  The evidence
is that all the T304 power meters show a one or two dB dip
at each scan.  Since it is seen in the input power meter it
must be happening upstream of the downconverters.