Microwave radiation from Zero Field singularities in stacks of two long Josephson junctions

We present experimental results on the radiation emitted from two-stacks of long Josephson junctions with double overlap geometry. Microwave radiation was received from the voltage-locked Zero Field Steps of the c(-) family, corresponding to fluxon-antifluxon pairs oscillating in the stack. It was a lso received from other current singularities, interpreted as resonances ex cited by the magnetic field generated by the nonuniform bias currents. In t he former case, there is experimental evidence for an appreciable signal, w hile, theoretically, the net signal produced is expected to be vanishingly small. This event can be explained in terms of a possible delay between the component signals, as the junctions in the stack do not have identical len gth.