Volume 410, Number 3, November II 2003
|Page(s)||1089 - 1100|
|Published online||17 November 2003|
Offset balancing in pseudo-correlation radiometers for CMB measurements
IASF-CNR, Sezione di Milano, Via Bassini 15, 20133 Milan, Italy
2 Università degli Studi di Milano, Via Celoria 16, 20133 Milan, Italy
3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
4 Jodrell Bank Observatory, Jodrell Bank, Macclesfield, Cheshire SK11 9DL, UK
5 University of California at Santa Barbara, Physics Department, Santa Barbara, CA 93106, USA
Corresponding author: A. Mennella, firstname.lastname@example.org
Accepted: 7 August 2003
Radiometeric CMB measurements need to be highly stable and this stability is best obtained with differential receivers. The residual 1/f noise in the differential output is strongly dependent on the radiometer input offset which can be cancelled using various balancing strategies. In this paper we discuss a software method implemented in the PLANCK-LFI pseudo-correlation receivers which uses a tunable gain modulation factor, r, in the sky-load difference. Numerical simulations and experimental data show how proper tuning of the parameter r ensures a very stable differential output with knee frequencies of the order of few mHz. Various approaches to calculate r using the radiometer total power data are discussed with some examples relevant to PLANCK-LFI. Although the paper focuses on pseudo-correlation receivers and the examples are relative to PLANCK-LFI, the proposed method and its analysis is general and can be applied to a large class of differential radiometric receivers.
Key words: cosmology: cosmic microwave background, observations / instrumentation: detectors / methods: analytical
© ESO, 2003
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