Intro: (top)

    The cband receiver has always been a native linear receiver. back in jun05 ganesh built a polarization switch box that would change from linear to circular using a hybrid.
We are now discussing putting a hybrid in the new 4-8 ghz receiver to allow the vlbi users to generate the circular polarization that they need. NRAO uses a hybrid in the dewar before the lna. Another option  is to put a hybrid after the dewar.
    Rumor has it that ganesh's attempt to put a hybrid after the dewar (back in 2005) did not work very well. I'm now trying to resurrect those measurements.

Documents found on maestro:

• schematic circa 2004 (.pdf)
• Looking through our stock room, it looks like the quad hybrid was:
• MAC Technology c7205 hybrid
  
• ./Receiver Group/From Ganesh Sept 2012/Rx_2005/CB_Upgrade_AprMay2005/CB_polbox
• 09may2015. looks like measurements of the polBox in the lab with the network analyzer
  
• The first 4 look like the s parameters for the box in linear (straight through) and circular (hybrid in)
  
• CH_A_CIR.png
• CH_A_LIN.png
• CH_B_CIR.png
• CH_B_LIN.png
• The next 2 look to be the phase shift input -> other output with hybrid in (i think this should be +/- 90 deg).
  
• PHASE_Ain_Bout RATIO.png
• PHASE_Bin_Aout RATIO.png