  This paper is part of the Prelaunch status LFI papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jinst .
  This paper describes the impact of the Planck Low Frequency Instrument front
end physical temperature fluctuations on the output signal. The origin of
thermal instabilities in the instrument are discussed, and an analytical model
of their propagation and impact on the receivers signal is described. The
experimental test setup dedicated to evaluate these effects during the
instrument ground calibration is reported together with data analysis methods.
Finally, main results obtained are discussed and compared to the requirements.
