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CARMA, and the CARMA WVR effort

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). Outline. What is CARMA?

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CARMA, and the CARMA WVR effort

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  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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