  We experimentally study the synchronization of two chaotic electronic
circuits whose dynamics is relayed by a third parameter-matched circuit, to
which they are coupled bidirectionally in a linear chain configuration. In a
wide range of operating parameters, this setup leads to synchronization between
the outer circuits, while the relaying element remains unsynchronized. The
specifics of the synchronization differ with the coupling level: for low
couplings a state of intermittent synchronization between the outer circuits
coexists with one of antiphase synchronization. Synchronization becomes in
phase for moderate couplings, and for strong coupling identical synchronization
is observed between the outer elements, which are themselves synchronized in a
generalized way with the relaying element. In the latter situation, the middle
element displays a triple scroll attractor that is not possible to obtain when
the chaotic oscillator is isolated.
