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Large Sky Dip Calibration Runs

Large Sky Dip Calibration Runs. Taken once per Day. Lasts ~ 15 minutes long. Telescope elevation varies by 40 degrees. Calibrates the “Leakage” and relative Total Power Gain between Diodes. Using atmospheric modeling, can calibrate the Absolute Total Power Gain of a Diode.

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Large Sky Dip Calibration Runs

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  1. Large Sky Dip Calibration Runs • Taken once per Day. Lasts ~ 15 minutes long. • Telescope elevation varies by 40 degrees. • Calibrates the “Leakage” and relative Total Power Gain between Diodes. • Using atmospheric modeling, can calibrate the Absolute Total Power • Gain of a Diode. • Note that Mini sky Dips are taken in between CMB Patch Scans.

  2. Sky Dip Calibration Q1 Total Power (mV) for Module 00 Phase switches off Telescope Elevation (degrees) phase switches on time (5 second bins)

  3. Q1 Module 00 total power Phase Switch Turned off Plotting only Phase Switch = ON

  4. Q1 Total Power versus Elevation Our ADC has a “reversed” Proportionality. Need conversion from mV to Kelvin (aka “gain”). Gain is derived from “Sky temperature” model, and confirmed with TauA observations. Gains for each diode is stored in database. For Q1 module 00, gain ~ 2.6 mV/Kelvin 2 kelvin excursion in sky temperature Less atmosphere More atmosphere

  5. Atmospheric Contribution to Noise (tuned for QUIET)

  6. ROUGH Calibration Assume* T(zenith) = 5 Kelvin Then T(sky temperature) = T(zenith)/sin(elevation) Then Gain = 2.9 mV/Kelvin Kelvin * in reality, there is dependence on PWV and actual air temperature.

  7. Example: Estimate of Noise Temperature for Q1 Module 00 ADC (Phase switches Off) = 2300 mV ADC (85 degree elevation) = 2039 mV difference = 2300 – 2039 = 261 mV Gain (Q1 Module 00) = 2.9 mV/Kelvin Measured Power = 261/2.9 = 90 Kelvin CMB Noise Power = 3 K Atmospheric Noise Power ~ 5 K Noise seen at Diode ~ 90 – 3 – 5 = 82 Kelvin

  8. “I to Q” Leakage 0.2 mV / 7 mV = 2.8 % Total Power Q1 Double Demodulated Q1 7 mV 0.2 mV

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