CARMA BandPass Stability (ct003)

Kim Nguyen, with Peter Teuben, Marc Pound and Lee Mundy have started bandpass stability tests in August 2010. This project is part of the CARMA Array Health Tasks. This page reports on their progress.

A note on naming convention: bandpass vs. passband. The MIRIAD item is called bandpass, but you will often also find the name passband uses in source code and script names.

  1. An observing script arrayHealth/ was created Oct 22, 2010, and can be used to produce ct003.passband.* datasets. It was cloned off arrayHealth/
  2. A script was written to provide functions to analyze passbands. e.g.


bandpass gains: amplitude (left panel, scale at bottom) and phase (right panel, scale at top, in degrees). This is for a 500 MHz, window, with 95 channels (vertically) and 15 antenna (horizontally) array. This example is for the noise source.

Report: Sept 2, 2010

First we measured the variations of the antenna based solutions of
typical 2" integrations of the noise source.  
There are two types of data available in the archive:
- fringetest:  usually 6 samples of 2" integrations preceding the
  	       calibrator, 1 minute of 2" integrations now??
	       used to be 10"
  The correlator is usually set up with 8 500MHz bands spread out
  over about 4-5 GHz in the IF.

- science data: usually 1 sample of 2" each time before a calibrator
  The correlator setup varies, depending on science track.

mfcal bandpass solutions are computed, and a Ant-Chan-Time cube
for phase and amplitude is created. For each Ant-Chan point a time
averaged value is subtracted, and the variations in this cube
are given as an indication of the stability.

- 6 sample fringetests consistently show amp variations 2e-4 
  and phase variations 0.1 degrees

- a 2-3 hour science track show different variations:
  * amp 4e-3   phase 0.7 deg   for noise,c0566    2" over 2-3 hrs
  * amp 0.04   phase 3         for 3c454.3,c0566  30" over 15 mins
  * amp 4e-4   phase 0.2       for noise,c0645    2" over 2-3 hrs
  * amp 0.03   phase 3         for 3c273,c0645    30" over 15 mins

   - the noise source sometimes does go wacko
   - after subtracting mean banding - array health - can be used.

PJT 2-sep-2010