Abstract
In this paper we study peculiarities of behaviour of a nematic liquid crystal (NLC) in an electric field consisting of two harmonics with different amplitudes and frequencies. The most interesting result is the experimental observation of high frequency, stabilization of a low frequency electrohydrodynamic instability in the NLC. A method of measurement of the one frequency instability threshold has been proposed. The beating regime of the two frequency electric field was also studied. The theory developed provides an explanation for all the experimental results.