Intro

    When looking at the sun with xband, we found that the synth chassis of the udc was going into saturation.

• 29oct21: udc saturates on the sun
• 19nov21: udc linearity test
• 04apr22: 15,20db pads (sol  atten) now switchable)
  
• 06apr22:power levels on,off the sun with solar atten in,out.

    We installed swithable attenuators before the udc on 04apr22

• PolA 15 db
• PolB  20 db

    Whenever solar observations are done, software  inserts these attenuators into the rf chain

•  tcl cmd: attn asol 0/1  (out,in)

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16Feb23: Solar atten increases xband Tsys.

    Xband astronomical observations have occasionally had saturation problems from:

• rfi covering 8732 to 8968 (more info)
• This was  mapping cygnus in jun-jul22

    Project a4004 is doing crosses at xband and also saw some saturation across the entire band when the 8732-8968 MHz rfi was strong.
A test was made to see whether installing the solar attenuator (before the udc unit that saturates) would stop the saturation.

    The test had:

•  a cross had a 1 deg azimuth strip in 1 minute (600 samples) followed by a 1deg elevation strip.
• 7 172 MHz bands were taken covering the xband receiver.
• 1024 channel spectra were dumped at 10Hz.
  
• 10 crosses were done with the solar attenuator out
• then 10 crosses with the solar attenuator in
• we adjusted the gain after the udc to get the sample levels going through the if/lo and into the mocks.
• the total power at each sample was then computed (after throwing out rfi).
• Unfortunately the rfi did not appear during this test.
  
• What we could do was compare the Tsys with the attenuator in with the attenuator out.
  

    The plots show the results of the tests (.ps) (.pdf)

• the total power from the 10 crosses were plotted (600smp x 10 crosses) after using the cals to convert to deg K.
• Black is the Tsys measured with the solar attenuator out
• red is the Tsys with the solar attenuator in.
• The vertical dashed lines separate the 10 crosses.
• page 1-7: total power vs sample for each of the 7 freq bands.
• Top: polA
• bottom: polB
• The red (atten in) was taken about 30minutes after the start of the black lines (attenuator out).
• Tsys changes with the solatten in or out
• Tsys changes:
  
• polA about 10 to 15 K with atten in
• polB 5 to 10 K higher with atten in.
• pages 8-9L avg tsys vs elevation
• Average tsys vs elevation
• Tsys was averaged over each az strip
• Black atten out, red atten in
• This checks if the tsys difference was from the change in elevation (doesn't look like it).

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Summary

• Using the xband receiver tsys was higher when the solar attenuator was in the path.
• polA - 10 to 15 K higher with atten in.
• polB   3 to 10 K higher with  atten in.