EDP Sciences
Free access
Volume 410, Number 3, November II 2003
Page(s) 1089 - 1100
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20031266

A&A 410, 1089-1100 (2003)
DOI: 10.1051/0004-6361:20031266

Offset balancing in pseudo-correlation radiometers for CMB measurements

A. Mennella1, M. Bersanelli2, M. Seiffert3, D. Kettle4, N. Roddis4, A. Wilkinson4 and P. Meinhold5

1  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

(Received 26 March 2003 / 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

Offprint request: A. Mennella, daniele@mi.iasf.cnr.it

© ESO 2003