  Transport properties of two coupled Josephson junctions driven by ac currents
and thermal fluctuations are studied with the purpose of determining dc voltage
characteristics. It is a physical realization of directed transport induced by
a non-biased zero averaged external signal. The ac current is applied either to
(A) only one junction as a biharmonic current or (B) is split into two simple
harmonic components and separately applied to respective junctions. We identify
regimes where junctions can operate with the same as well as opposite signs of
voltages. A general observation is that in the same parameters regimes, the
scenario (B) is more efficient in the sense that the induced dc voltages take
greater values.
