lbw polB cal jump on 23apr04
The system temperature for lbw jumped in 23apr04.
At 2am polA, polB were the same. At 18:30 the temperatures were different
by 20 percent. on off position switching was done on two unpolarized continuum
source. If the jump was in Tsys (the cals were ok) then the source
deflection in kelvins should have been the same for polA and polB. If the
jump was a change in the cal value, the the source deflections for the
two sources should differ in polA and polB.
The source were 3C232 and 4C32. The measurements
used 1415 and 1665 Mhz with the feeds native linear mode. The source
There were 10 measurements of the two sources. 4
on 23apr04 evening and 6 more on 24apr04 evening. The
plot shows the results (ps) (pdf)
Fig 1 Top: Tsys versus day of year for 2004. Different colors used
different cals to measure Tsys. The solid lines are polA while the dashed
lines are polB. You can see the jump on 23apr04 in the dashed lines (polB).
It continued increasing for awhile and started to come dow around 24may04.
This data was taken at 1400 Mhz.
Fig 1 Bottom: This plots the ratio TsysB/TsysA and TsrcB/TsrcB for
10 on/off measurements done on the continuum sources 3C232 and 4C32. 4
measurements were done on 23apr04 and 6 more were done on 24apr04. The
coding for the plot is:
Tsys polB jumped on 23apr04 between 2am and 18:30. It wandered up and then
down by a few kelvins for a month. During this time period Tsys for polA
Looking at the sources, you can see that the polB/polA ratio is about 1.2
for the polB/polA source deflection and for the ratio of TsysB/TsysA
(for both sources). Since the source deflection ratio should be unity (since
the sources are unpolarized) the difference is a change in the cal
values and not a real jump in Tsys polB. The large variations in the red
trace is from interference.
The jump is a function of frequency. The 1665 Mhz ratio is 1.11 while the
1415 Mhz ratio in 1.18.