resonances in the cband receiver


    The cband receiver was searched for resonances in the omt by doing 1 minute on/off position switching on VirgoA. See resonances in the lbw receiver for a description of the technique. The resonance signature of cband will be different than lbw and sbw. The omt of lbw,sbw is at 70 K while the cband omt is at 20K. The Off positions will not have a bump at the resonance since the  omt 20K temperature is close to that of the scattered radiation coming in through the horn. There should still be a dip in the on position if the source is stronger than 20 Kelvins.
    Virgo A was chosen because it was the only strong source available during the test time. It is actually too strong and extended. It did not give very good band passes. The correlator was run with 4 by 25 Mhz bandwidths overlapping each sbc by 2.5 Mhz. The band was measured in 80 MHz junks from 3920 Mhz to 5675 Mhz.  It took 22 measurements to cover the range. The frequency scans needs to be continued to 6 Ghz when time becomes available The plots show the results:
  • Fig 1 PolA and  Fig 2 PolB show on/off -1 normalized to the median  value in each sbc. The 22 different measurements are over plotted. The 4 frames are the 4 sbc. The band passes look similar except for:
  • the top plot blue line at -10 Mhz. This is 4160.5 Mhz.
  • The 3rd frame from the top with the light blue line dipping at -6 Mhz. This is 5246.5 Mhz.
  • The bottom frame has the red line dipping at 6 MHz (5676.5Mhz) and the green line at +10 Mhz (4160.5Mhz).
  • The 3rd figure plots the individual band passes with the resonances. The black line is polA and the red line is polB. The two blue lines are the polA band passes +/- 80 MHz from the resonance bandpass.

    Resonances found
    4160.5 Mhz
    5246.5 Mhz
    5676.5 Mhz

        The resonances probably extend farther in frequency when doing polarized measurements  (stokes q,u,v). The observations should be repeated on a strong point source.

    processing: x101/020729/