lband wide polB instability jul10
09sep10
Project a2335 saw an instability in polB
during their data acquisition in jul10. Their setup was:
- lbw in linear pol mode, 1230-1470 filter as well as 1280 hipass
filter.
- 300 sec on,off position switching
- freq around 1360-1380 Mhz
- interim correlator, 9 level, 1 second dumps with 4 boards:
- band 1 12.5 Mhz polA
- band 2 12.5 Mhz polB
- band 3 25 Mhz polA,polB
- band 4 25 Mhz polA,polB
The plots show the instability
in polB (.ps) (.pdf):
- Top total power vs time .. raw data
- black is pola, red is polB, green separates the 300 second scans
- The vertical units are correlator power.
- changes in total power also occur because:
- change in za
- changes in correlator attenuation (around rec 2400 polA)
- Middle: Normalize each 300 second scan to its median value
- You still see the za change.
- polB drifts off around record 70
- Bottom: divide normalized PolB by normalized polA
- The Tsys variation has been removed.
- Pol B is varying by about 4% of Tsys
processing:
x101/100909/lbwinstabilty.pro
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