Figure 1
From: Design, Analysis, and Performance of a Noise Modulated Covert Communications System
(a) Transmitter block diagram, (b) receiver block diagram. (AMP  =  amplifier, BPF  =  bandpass filter, DL  =  delay line, FPGA  =  field programmable gate array, H  =  horizontal, OSC  =  oscillator, PD  =  power divider, SSB  =  single sideband, V  =  vertical).