  Fluxon transmission through several impurities of different strength and type
(i.e., microshorts and microresistors), placed in a long Josephson junction is
investigated. Threshold pinning current on the impurities is computed as a
function of the distance between them, their amplitudes and the dissipation
parameter. It is shown that in the case of consequently placed microshorts or
microresistors, the threshold pinning current exhibits a clear minimum as a
function of the distance between the impurities. In the case of a
microresistor, followed by a microshort, an opposite phenomenon is observed,
namely the threshold pinning current exhibits maximum as a function of the
distance between the impurities.
