There are several levels of fidelity that can be used based on the requirement of the simulation.
Ranging can be disabled, which eliminates noise effects, but still requires frequency/modulation/frequency hopping/and or crypto matching as implemented.
The audio noise can be turned off, so there is ranging, but no audio noise in the signal (i.e., it will simply cut off when out of range).
Basic radio operation implements ranging, and noise effects and includes line-of-sight WSG84 curved Earth occulting.
Occulting may be linked to an external database (maybe provided by a visual system or radar simulation) such that a higher fidelity occultation model based on terrain may be linked or the ASTi Terrain server may be used to provide the database interface.
The HF frequency range (2MHz to 30MHz) may be modeled to a high fidelity to include ionospheric effects, based on time of day, sun spot cycle, time of year, etc using the ASTi HF server.