[evlatests] antenna 18 x-band: poor sensitivity

[Michael Rupen]

Hi --

   Tsys for ant. 18 at X-band was reasonable (40 K-ish and stable) on
Nov. 16, 17, 18, 21, 22, 24, and 25. On the 26th, Tsys for ant. 18 showed
a steady secular decline on all IFs from ~100 to ~60 K, from 23:00 to
23:50 IAT.  Could this be something like residual ice?  The C band Tsys for 
ant. 18 just before this (20:20-22:20) looked quite reasonable, steady at
~35 K.

   Ant. 18 has shown many phase jumps both at C and X bands (maybe others,
I haven't checked) for at least a couple of weeks now.  Because of that
I haven't gone far enough in calibration to check the sensitivity, apart
from noting that it seems roughly in line with the other antennas in terms of 
rms noise and gain.

             -- Michael


On Wed, 28 Nov 2007, Charles Kutz wrote:

> It appeared to be ok about a month ago. We are sending teams out to all
> arms today checking/verifying all EVLA feed heater operations. We will
> take special note of 18.
>
> Chuck
>
> Emmanuel Momjian wrote:
>> The test observations of yesterday (Nov. 26) showed that the sensitivity
>> of antenna 18 at x-band and at all IFs is low by a large factor due to
>> high system temperature values, which are between 140 and 190 K.
>>
>>
>> _______________________________________________
>> evlatests mailing list
>> evlatests at listmgr.cv.nrao.edu
>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
> _______________________________________________
> evlatests mailing list
> evlatests at listmgr.cv.nrao.edu
> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>