VOACAP

VOACAP, or Voice of America Coverage Analysis Program, is a free, internationally recognized radio propagation model used for predicting High Frequency (HF) radio signal coverage. Developed by the Voice of America (VOA) and later maintained by NTIA/ITS (National Telecommunications and Information Administration / Institute for Telecommunication Sciences), it calculates the signal strength and reliability of radio communications over long distances, taking into account factors like ionospheric conditions, frequency, antenna characteristics, geographic location, and time of day.

VOACAP predicts signal-to-noise ratio (SNR) and the probability of communication success for a given HF radio path. It’s primarily used by broadcasters, amateur radio operators, government agencies, and military organizations for planning and optimizing HF radio communications.

The model leverages empirical data and statistical methods to estimate ionospheric propagation, accounting for phenomena such as refraction, absorption, and reflection within the ionosphere. It outputs predictions in the form of signal strength values, MUF (Maximum Usable Frequency), LUF (Lowest Usable Frequency), and path reliability.

VOACAP differs from other propagation models in its approach to ionospheric modeling and its emphasis on providing probabilistic predictions rather than deterministic results. Its widespread use and relatively accurate predictions, particularly under varying solar conditions, have established it as a standard tool in the HF radio communications community. While initially developed with a focus on shortwave broadcasting, VOACAP has been adapted and applied to a variety of other HF communication scenarios.