  We study the stochastic resonance phenomenon occurring in electronic Chua
circuits operating in the chaotic regime when the forcing signal is modulated
at relatively high frequency, of the order of magnitude of the main Chua
frequency in the absence of forcing ($f_o$). In all the cases, a clear maximum
in the signal-to-noise ratio for an intermediate noise level is observed. When
modulating with a frequency smaller than $f_o$ we also observe a resonance at a
harmonic of the external frequency which is closer to $f_o$ or to one of its
harmonic. If the modulating frequency is larger than $f_o$ we only observe the
resonance at the modulating frequency.
