The FDX is a diplexer designed to examine signals having harmonic frequency components of the transmitting pulse. Normally diodes are used in diplexer construction. When studying nonlinear phenomenon, this is unacceptable because diodes are very nonlinear components. Therefore, RITEC has designed a diplexer that protects the receiver from the high-power, low-frequency driving pulse while allowing the higher-frequency harmonics to be received. It is normally used for the odd harmonics because transducers are typically more sensitive to these frequencies. The FDX is designed for operation at a specific fundamental frequency that is specified by the user.