SBN SEFD RATIO POLA/POLB
The system temperatures for polA,polB on sbn differ
by about 5K (dec 2002). This could be a problem in the cal values or it
could be a real difference in the system temperatures. To test this, 3
sources were tracked using the heiles calibration scans on 23,24 dec02.
The Tsys and source deflection for each Pol were recreated ((I+Q)/2 , (I-Q)/2)
for each strip of each pattern. The SEFD was then computed for each polarization.
These values are independent of the cals. The ratio sefdA/sefdB is also
independent of the source flux. It only depends on the Tsys, gain of the
telescope, and polarization of the source. Since sbn is native circular
we assume that there is equal source flux in each polarization. If
the cals are correct, then the source deflection should be the same for
each pol while the system temperatures should differ. The plots
show the Tsys, Tsrc, and sefd ratio.
Top figure has the Tsys for all strips. Black in polA and read is polB.
They differ by about 5K.
Center figure is the source deflection in K. Pol A and polB are over plotted.
The values for the 2 polarizations lie on top of one another.
Bottom Figure shows the ratio of SEFDA/SEFDB vs za. A linear fit to the
data versus za gives an average value of 1.226. The ratio of TsysA/TsysB
is also plotted in green. This data falls within 1% of the sefdRatio.
The source deflection and sefd ratio show that the relative cal values
of sbn are correct and that the system temperature difference is real.