Frequency dependence of orthogonal polarisation modes in pulsars J. M. Smits, B. W. Stappers, R. T. Edwards, J. Kuijpers and R. Ramachandran A&A, 448 3 (2006) 1139-1148 Published online: 03 March 2006 DOI: 10.1051/0004-6361:20053259