The concept of a large-scale (gigantic) coaxial line, filled with partially ionized plasma and excited by a nanosecond-pulse generator, is proposed and implemented for laboratory simulation of the phenomena arising under propagation of ultrawideband electromagnetic pulses (UWB EMPs) in the Earth's atmosphere and ionosphere. The line makes it possible to study the waveform transformation effects of UWB EMPs due to dispersion and nonlinear effects in plasma (including in the presence of an external magnetic field). The line characteristics are demonstrated in a vacuum chamber of the large-scale plasma facility KROT. [ABSTRACT FROM AUTHOR]