Why VOACAP stands for Voice of America Coverage Analysis Program, a propagation prediction engine developed for planning international HF broadcast coverage. It uses ionospheric models plus solar indices (SSN or SFI), time of day, season, antenna patterns and power to predict signal strength and the probability of a usable circuit between two points on the HF bands. Hams use it to pick the best band and time for a given path, and it reports things like MUF and reliability percentages.
Watch out VHF propagation is tempting because VOACAP does produce coverage maps, but VHF paths depend on tropospheric ducting and line of sight rather than the ionospheric refraction VOACAP models. The AC voltage/current and impedance choices are circuit analysis, not propagation.
VOACAP: Voice Of America Coverage Analysis Program - shortwave broadcasting means HF.