Polarized Tsys using the alfa receiver

sept 2005


    Rotating the azimuth arm (section):
        (TsysA-TsysB) vs az for each pixel and za (.ps) (.pdf):
        2az amplitude and phase of maximum (.ps) (.pdf)
    Rotating the alfa feed system (section):
        TsysK, TsysDifK, and the fits versus rotation angle (.ps) (.pdf ) :


     Polarized components of Tsys have been previously measured with the lbw  , sbh, and cband receivers.  These tests were done by rotating the azimuth arm and measuring TsysA-TsysB versus azimuth. A sine wave of period 180 degrees and amplitude .2 to .5 kelvins was seen. The phase of the sine wave depended on the orientation of the feed probes (which differed for each feed).
    The alfa receiver has 7 feeds. It also has the capability to rotate +/- 90 degrees about the center pixel. All of the receiver probes have the same alignment direction. When the alfa rotator is at 0 degrees, the two probes (polA,polB) point +/- 45 degrees from the azimuth arm direction.
    Two sets of tests were done with the alfa receiver:

22aug05 TsysA-TsysB vs azimuth angle:   (top)

    TsysA-TsysB was measured versus za using the following setup: The data analysis was then:
  • For each az swing sample compute the total power over the 100 Mhz bandpass (throwing out outliers).
  • Scale the data to kelvins using the cals.
  • Compute TsysPolAK- TsysPolBK for all beams.
  • For each az swing fit yfit(az)=c0 +c1*az + c2*cos(az)+c3*sin(az) + c4*cos(2az)+c5*sin(2az).  The routine corblauto() was used for the fitting. It iterates the fit throwing out points greater than 3 sigma.
  •     The plots show the difference  (TsysA-TsysB) vs az for each pixel and za (.ps) (.pdf): The azimuth swings were done in the sequence: za= 5,10,15,19.5,17.5,12.5,7.5. The interference was probably caused by the sun.

        The coefficients of the 2az terms were used to compute the amplitude and the azimuth angle of the sine wave maximum. The 2az amplitude and phase of maximum (.ps) (.pdf) are plotted versus za.


    processing: x101/050822/azswing_fit.pro, azswing_inp.pro

    01jun05 rotating the alfa feed. (top)

        TsysA-TsysB was measured versus alfa rotation angle on 01jun05.  The azimuth arm was stationary at 270 degrees (dome in the west) and the zenith angle was at 8.468. The rotator was moved from -90 to 90 in 100 seconds. 4 rotations were done (-90 to 90,90 to -90,-90 to 90, and 90 to -90). The wapps were run in pulsar mode with 100 Mhz bandwidth, 256 lags, centered at 1420 Mhz. The spectra were  sampled at a1 millisecond rate. The cals were cycled at a 25 hz rate (20 milliseconds on, 20 milliseconds off) synchronized with the 1 second tick.
        The processing was: The Pixel positions: -90 degrees start and +90 degree end are shown in the picture below. They are sitting on the feed array with up towards the secondary (and pointing west since az=270). The rotation was clockwise looking at these pictures.


     The plots TsysK, TsysDifK, and the fits versus rotation angle (.ps) (.pdf ) :


    processing: x101/050601/rotalfa.pro