2014 October 31 VEGAS testing

Overview

At L band, the baseline of the YY polarization was seen to be non-flat by Adam last week. We will test whether placing some absorber material on the feed removes this wobble.

Method

Data in TGBT14A _912_43, using Astrid script TGBT14A_912/Lband_lbw_modes, frequency switching
  • Scan 41 - Mode 12; WITH ABSORBER; noticed very high tsys, so restarted for the next scan
  • Scan 42 - Mode 12; WITH ABSORBER; still high Tsys but seems unavoidable, so plow on
  • Scan 43 - Mode 13; WITH ABSORBER
  • Scan 44 - Mode 11; WITH ABSORBER

All the above scans showed high Tsys, and both XX and YY baselines are not flat At lunch, the absorber material was removed.

Data in TGBT14A _912_43, using Astrid script TGBT14A_912/Lband_lbw_modes, frequency switching
  • Scan 69 - Mode 12; WITHOUT ABSORBER; Tsys returned to expected levels
  • Scan 70 - Mode 13; WITHOUT ABSORBER
  • Scan 71 - Model 11; WITHOUT ABSORBER

In the above scans, Tsys was returned to a normal level, however the YY polarization was seen to show a non-flat baseline, consistent with Adam's previous observations.

Results

Screen grab of getfs output for plnum=0,1 wtih absorber:
high tsys.png

Screen grab of getfs output for plnum=0,1 without absorber:
low tsys.png

It seems like the absorbing material is not going to be helpful for this purpose. Further tests are suggested, instead moving the subreflector in and out of focus to see if this removes the possible standing wave in the system.
Topic attachments
I Attachment Action Size Date Who Comment
high_tsys.pngpng high_tsys.png manage 19 K 2014-11-07 - 11:43 SamBates  
low_tsys.pngpng low_tsys.png manage 14 K 2014-11-07 - 11:42 SamBates  
Topic revision: r2 - 2015-01-27, RichardPrestage
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