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Advancements in CARMA WVR Correlation Radiometer: Insights from the Wettzell Workshop 2006

This presentation by Alberto Bolatto and colleagues provides an overview of the CARMA (Combined Array for Research in Millimeter-wave Astronomy) effort, detailing its correlation radiometer and comparing its performance to other arrays. The workshop covers the technical challenges faced, improvements in antenna reflectors, and expected performance metrics, including the impact of temperature control and spectral baseline removal. A focus is placed on the correlation receiver's stability and its effectiveness, with insights into enhancing the reliability of data capture in radio astronomy.

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Advancements in CARMA WVR Correlation Radiometer: Insights from the Wettzell Workshop 2006

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Presentation Transcript

  1. WVR workshop Wettzell 2006 CARMA, and the CARMA WVR effort Alberto Bolatto Associate Research Astronomer U.C. Berkeley Astronomy Radio Astronomy Lab Dick Plambeck (UCB/RAL), Dave Woody (Caltech), Leslie Looney, Yu-Shao Shiao (UI), Douglas Bock (CARMA)

  2. Outline • What is CARMA? • The OVRO experience • The RAL correlation radiometer • What next?

  3. Berkeley-Illinois-Maryland array 10 6.1-m diameter antennas CEDAR FLAT Caltech array 6 10.4-m antennas + UChicago SZA 8 3.5-m antennas

  4. Cedar Flat – elevation 2200m August 2005 June 2004

  5. 21 Jul 2004 – lifting off the first reflector

  6. panel adjustmentsurface error determined from holography before adjustment: 127 μm rms → 75% loss at 225 GHz after adjustment: 28 μm rms → 7% loss at 225 GHz

  7. all antennas assembled10 Aug 2005

  8. Comparison with other arrays

  9. Now E, D configurations baselines 8–150 m1mm beam: 2” 1.6 km

  10. for Winter 2005 E, D, C configurations baselines 8–350 m1mm beam: 0.8” 1.6 km

  11. for Winter 2006 E, D, C, B, B+ configurations baselines 8–1700 m1mm beam: 0.2” 1.6 km

  12. for Winter 2008 E, D, C, B, A configurations baselines 8–1900 m1mm beam: 0.13” 1.6 km

  13. 225 GHz zenith opacity Tsys computed for 1.5 airmasses, Trcvr(DSB) = 45 K

  14. OVRO WVR

  15. Sample phase improvement

  16. It can work, but… • Can it work reliably? • It’s easy to improve very bad tracks, but good tracks can be worsen • Only works for ~40% of the data Y.-S. Shiao et al., SPIE, (2006)

  17. Correlation WVR at 22 GHz • Correlation receiver: less sensitive to amplifier gain variations, no moving parts, built-in absolute calibration. Fast control of temperature of reference for nulling: ultimate stability. • Weak points: complexity, sensitive to spurious correlations

  18. Expected performance • Measured amplifier performance based on Hittite commercial HMC 281 GaAs mmic ($40): Tnoise ~55 K, G ~23 dB, BP ~16-36 GHz • Expect Tsys~ 140 K, or RMS ~5 mK in 1s in 1 GHz hot spill~3% (9 K), input w.g. loss~0.5 dB (32 K), hybrid+w.g./coax loss~0.3 dB (4 K), 2nd amp stage~5-10 K • Assuming canonical ~4.5 mm/K @ 22.2 GHz expect path RMS ~20 mm in 1s • Performance will be degraded by control of load temperature, thermometry, spectral baseline removal, etc, but there is a safe margin • /20 goal is ~60 mm

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