An EMP/HEMP protection device for protecting equipment from electromagnetic pulses. The protection device includes a housing defining a cavity therein and separated into two chambers, a dirty chamber for propagation of signals before filtering of electromagnetic interference, and a clean chamber, isolated from the dirty chamber, for propagation of signals after filtering. A rigid-flex printed circuit board (PCB) is disposed in the cavity for facilitating electrical connections between the chambers. Surface mount electrical components for EMP/HEMP protection are coupled with the rigid-flex PCB. Power and/or data signals are transferred from the dirty chamber to the clean chamber though a wave guide below cutoff (WBC). The WBC is formed from opposing electrical ground planes within a center PCB of the rigid-flex PCB. An electrically conductive and weather sealing gasket is disposed in the cavity of the housing for further EMI isolation.