Power levels in galfa pixel 2b changing
On 13jul05 project a2004 saw the power level in
pixel 2b changing in the data from the galfa spectrometer. Data was simultaneously
being taken with the wapp spectrometers. The wapps showed no jumping in
The plots show the
total power variation with time (.ps) (.pdf)
. This data was taken with the galfa spectrometer. There are 7 600 second
integrations shown (one per page).
You can see jumps or drifts in just pixel2b on just
about every page. The largest change is about 25% of Tsys.
Top Plot: Total power vs time for polA taken from the galfa narrow band
data. The 7 pixels are over plotted. The units are galfa counts (linear
in power). Each pixel is coded with a different color.
2nd plot: Total power vs time for polB taken from the galfa narrow
band data. Pixel 2b is green. You can see it start to decrease on page
1 around 200 seconds.
3rd plot: Pixel 2 for the galfa narrow band data is plotted by itself.
Black is polA, red is polB.
4th plot: Pixel 2 for the galfa wide band data. Black is polA, red is polB
When galfa pixel 2b drifted/jumped, the wapp pixel 2b did not change.
The plots shows the
wapp data when galfa pixel 2b drifted (.pdf)
The top plot is pixel 2A. Black is galfa, red is from the wapps.
The bottom plot is pixel 2B. You can see the galfa data start to decrease
near 8.26 hours while the wapp total power remains stable.
Pixel 2b of the galfa spectrometer is drifting by up to 25% of Tsys.
The changes can be slow drifts (3 minutes) or more sudden jumps.
When pixel 2b in the galfa spectrometer drifts/jumps, pixel 2b in the wapps
does not change so the problem is not in the front end. It has to be at
or after the downstairs distribution amplifier. I looked at the cables
from the receiver room over to galfa, and the cables in front of the galfa
spectrometer. I found no loose cables.