  In this paper we discuss the linearity response of the Planck-LFI receivers,
with particular reference to signal compression measured on the 30 and 44 GHz
channels. In the article we discuss the various sources of compression and
present a model that accurately describes data measured during tests performed
with individual radiomeric chains. After discussing test results we present the
best parameter set representing the receiver response and discuss the impact of
non linearity on in-flight calibration, which is shown to be negligible.
