Terrestrial free-space optical (FSO) links are based on the fundamental idea of a light beam transporting information, enabling extremely high data rates. Fog still presents a significant obstacle to enhancing the availability and dependability of terrestrial FSO lines because the fog particles scatter the light as it travels and only significantly attenuate the signal. Using a hybrid network with an FSO link and a backup link will solve the problem. GHz offers outstanding performance in this frequency band. In this research, the attenuation caused by fog is predicted using an empirical model based on measurements of visibility and their impacts on FSO/RF links. Multiple functioning FSO and RF links operating at 1 GHz, 10 GHz, and 25 GHz, as well as visibility, were simultaneously monitored for changes in signal intensity. The bit error rate (BER) for the optical modulation formats NRZ-OOK, L-PPM, and RZ-OOK is investigated under various fog scenarios. According to the results of the simulation, RF link performance at 25 GHz is better suited for hybrid system fog weather circumstances. On the other hand, we discuss the appropriateness of fog models within these various modulation formats. © 2023 Walter de Gruyter GmbH, Berlin/Boston 2023.