Polarized Tsys using the sbh receiver
may 2003
Polarized components of Tsys have been
previously
measured with the lbw
and cband
receivers. On 16may03 measurements of tsys were done using sbh (3
to 4 Ghz linear feed) to see how the component changed with frequency.
The setup and processing was:
run the correlator with 25 Mhz bandwidth, at 3200,3400,3600, and 3800
Mhz,
sampling at 1 second intervals.
drive the telescope in az at .2 deg/sec (half slew) from az 270 to 630.
Do this at za=2,4.5,7,9.5, and 12 deg (reversing direction on each
swing).
Fire the cal 3 times during the measurements to convert to kelvins.
For each az swing compute TsysPola TsysPolB.
For each az swing fit yfit(az)=c0 +c1*az + c2*cos(az)+c3*sin(az) +
c4*cos(2az)+c5*sin(2az).
Use the routine corblauto() for the fitting. This routine iterates the
fit throwing out points greater than 3 sigma.
The data was taken 11:45 to 14:20 hours so there is interference from
the
sun as well as continuum sources.
The plots show the difference TsysATsysB
vs az and za for this dataset:

Fig 1. (TsysATsysB)  median(TsysATsysB) is plotted vs azimuth for
each
swing. Each za strip is coded by color. The four boxes correspond to
the
frequencies 3200,3400,3600, and 3800 Mhz. The large drop at az of 200
degrees
is caused by the sun.

Fig 25 show the 2az fit to the data for frequencies
3200,3400,3600,
and 3800 Mhz. The black lines are:
(data(az)(c0+c1*az+c2*cos(az)+c3*sin(az))/
The red lines are the 2az fit. The green * are the points that were not
used in the fit. Each figure shows the five az swings at za
2,4.5,7,9.5, and 12 degrees.

Fig 6. This plots the amplitude and phase of the 2az fit versus za for
each frequency. The phase phi (lower plot) is defined as :
y=Amp*sin(2*azphi).
When az=phi/2 then the amplitude of the sine wave is 0.
Conclusions:

sbh has a .2 Kelvin polarized component to Tsys. This compares to
a .5 Kelvin value at 5 Ghz and .2 to .3 K at lbw. These values depend
on
the accuracy of the cals.

The phase is decreasing with za. The phase angle can not be compared
directly
with the cband and lband measurements since the angles of probes
relative
to the ground/sky is different for each receiver (although out
polarization
calibration should measure this using a well known polarized source).
processing: x101/030516/sbhswing/poldif.pro
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