• A 830MHz Sine wave was injected via the if2noise source input (there was only a sinewave, the noise was disconnected).
• This sinewave was mixed to with a 1Ghz lo to 170MHz.
• The power was measured using the if2 power meter sitting on beam 5.
  
• This signal was then sent to the bbmixers via the normal path.
• The signal was only injected into the low band. Beam 1 had no signal since that synthesizer was used to generate the birdie.
• Before the sine wave was injected, the gain levels in the bbm were adjusted to give a 30 count rms on input noise. This is the nominal setting for  using the spectrometer so the compression levels should reflect what occurs during normal observing.

• Each plot has 4 traces: black(polAI), red(polAQ), green(polBI), blue(polBQ).
• Page 1: A/D rms (in counts) vs bbm input power. We got to an rms of 1400 with close to 1dbm input.
• Page 2: base band mixer compression vs input power.
  
• A linear fit was done to 20*alog10(atodrms) vs bbm Input power. The last two points were not used in the fit.
• The data -fit was plotted to see where the compression set in.
• The residuals start to fall off above -1 dbm At 1dbm it is close to 1db compression.
• -1 dbm is flagged for reference
  
• Page 3: A blowup of the Peak A/D counts vs input power.
• this shows how much of the digitizer range we use before compression sets in.
• at -1dbm the a/d peak values are 1400 to 1700. This is compression free.
• at 1dbm the a/d peak values are 1800 to 2047. This is near 1db compression.

Conclusions:

• Using a sine wave the bbm starts to compress around -1 dbm with 1 db compression around 1dbm
• The A/D's have a peak value of 1400 to 1700 counts before compression starts. The A/D values for 1db compression is 1800 to 2047.
• We could remove 6db of attenuation from the bbm output stage. This would increase the compression free range of the A/D but it doesn't look like it will gain us much.
  

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