What does VOACAP software model?

VOACAP stands for Voice of America Coverage Analysis Program. It is a well-known, professional-grade software tool originally developed to predict high-frequency (HF) skywave propagation for Voice of America broadcasts. Amateur radio operators now widely use it to forecast the best times and frequencies for establishing HF contacts between two points on Earth. The software relies on various parameters like sunspot numbers, time of year, and station locations to model the ionosphere. It does not model VHF propagation, which relies on different phenomena like tropospheric ducting or line-of-sight propagation, nor does it have anything to do with alternating current (AC) voltage or impedance.