  A system scheme is presented which allows non-reciprocal wave transmission or
directional amplification of electromagnetic signals, using a boxed four-node
method. Edges represent strong hopping interactions and diagonals stand for
weak parametric interactions. Using careful optimization of values for design
parameters, we are able to obtain non-reciprocity in excess of 12dB and 130dB
for intrinsic and extrinsic configurations at identical input/output
frequencies. For the directional amplification, an isolation as high as 40dB is
demonstrated with forward/backward gains of $\pm$20dB. Cascading two such
systems potentially can offer high isolations at high gains.
