Intro

    When doing strips across the sun (on 28oct21) we saw compression in the signal. It was much worse in polB.
On  29oct21 we looked at whether the udc (up down converter) could handle the power levels when we were on the sun

    The udc has 2 chassis  (udc schematic .pdf)

• chassis 1 has the up down converter.
• chassis 2 has the 4 way splitter with the 15.5 db variable attenuators (in .5 db steps)

Update: 09nov21 added 15db, 20db pads to polA,polB at input to udc.

---

The test setups:

• the sun was tracked during the tests.
• The if2 power meter was used to measure the power levels.
• The attenuation in the if2 was set to 0 0  (attn if2 0 0)
• the power meter has a 20db pad in front of it.
• The if2 power meter received the signal from the 1-2 GHz output of the udc.
• Test 1:vary the udc attenuator
• this tested the dynamic range of the amps in the 2nd chassis.
• step the attenuator  15.5,10.5,5.5, and 0.5 reading the power meter at each step
• Test 2: test the first chassis.
• An external variable attenuator was placed in front of the udc input.
• it was stepped from 0 to 20db.
  
• the udc attenuator was left at 15.5 db attenuation during this test.

The plots show the results of the 2  tests. (.ps) (.pdf)

• Page 1: test the  2nd chassis by stepping the udc attenuator
• The attenuator was set to : .5,5.5,10.5,15.5 db
• Black is polA, red is PolB. green is a linear fit to the 10.5,15.5 db values
• Top: power meter reading vs attenuator setting.
  
• The power read went from -10.5 to - 23.5 db.
  
• Removing the 20db pad would have the power at the if/lo input be 9.5 to -3.5 dbm.
• Bottom: Measure power - linearfit.
• A linear fit was done to the 2 values measured at 10.5 and 15.5 db attenuation.
• Page 2: Test the 1st chassis dynamic range with an attenuator in front of the chassis.
• a variable attenuator was placed at the input to the udc.
• The udc attenuator (in chassis2 was left at 15.5 db attenuation).
• Top: if2Power meter reading vs attenuator setting.
• black polA. atten settings were:[0,5,10,15,20] db
• red :polB. atten settings were 1db steps  0 to 10 and then 15, 20db atten.
• The green lines are linear fits to the 10,15,20 db atten values.
• Bottom: Measured power - linearFit
• a linear fit was done to the [10,15,20] db atten settings and then subtracted from the if2power meter reading.
• PolB has started to compress with atten values less that 10db
• polA  has a smaller attenuation.

---

SUMMARY:

• While tracking the sun, attenuator settings were stepped to see if the system remained linear
• test1: chassis2.
• the chassis was linear. the max input power at the if2power meter (removing the 20db pad) was 9.5 dbm.
  
• the udc output was higher that this because of the cable loss udc to if/lo rack.
• test2: chassis1.
• This showed compression until an attenuation of 10db was placed in front of the udc.
  
• So the compression seen in the sun mapping (28oct21) was partially occurring in the 1st chassis of the udc.
• You would expect that both pols should compress at similar levels.
• We need to check which component is  saturating in the 1st chassis of the udc.
  

---

processing:x101/211029/chkudc.pro