Galfa pixel 4a/6a switched jul05
The cables for pixel4a and pixel6a (count from 0)
from the distribution amplifiers in the receiver room to the galfa spectrometer
were switched on 11jul05 (after 8 am AST). They were returned to
the normal order on 19jul05 (12:00 AST). The data going to the wapps were
never switched. This meant that when looking at the galfa data off
This was the same problem that occurred back in may05. The distribution
amplifiers in the control room were removed to install the second fan (the
first was installed back in may05). When the chassis was reinstalled, the
cables leaving the chassis (going to galfa) were switched.
pixel 4a spectra would be in the location of pixel6a
pixel 6a spectra would be in the location of pixel4a.
Continuum sources drift/move through the alfa beams
at different times since the beams point at different locations in the
sky. 600 second total power scans showed that pixel 6a and pixel
4b had continuum sources moving through the beams at the same time (6b
and 4a also showed this).
On 11jul05 a2011 took data using the wapps and using
galfa. The plot shows the total
power drifts versus time after the cable switch (.ps) (.pdf).
Each pixel is plotted in a different color.
This problem only affected the galfa spectrometer. The wapp data was never
Fig 1 wapp data. The top plot has the 7 pixels for polA. The bottom plot
is polB. The light blue trace is pixel 6. A continuum source moves
through pixel 6 around 18.981 hours. The source appears at the same time
in polA and polB.
Fig 2 galfa data. The top plot has the 7 pixels for polA. The bottom
plot is polB. The continuum source at 18.981 is now in pixel 4A and pixel
6B. It should have been in pixel 6A and 6B.
The galfa cables for pixels 4a, 6a were switched on 11jul05 between 8 am
and 16pm (ast).
The cables were put back in the proper order on 19jul05 at 12:00 pm (ast).
The wapp alfa data was not affected by this problem.
When processing galfa data for this date range, you should interchange
the spectra for pixel 4a and pixel 6a. The value in the data headers should
not be changed.