Kim, David SThe characterization and switching system for a hybrid Free-Space Optical (FSO) with Radio Frequency (RF) backup link is described. Such hybrid systems are used to take advantage of the large bit rates achieved with FSO while maintaining high reliability with a RF backup. In this project, monitoring and switching are controlled by a program that checks the FSO connection health using echo packets. The switching program was tested using a fiber optic link that can simulate atmospheric attenuation effects, such as scintillation, by using an optical modulator. The system's sensitivity to connection quality degradation and momentary connection outages can be optimized for a given situation. The simplicity and ease of implementation are the main strong points of this system.en-USThesisEngineering, Electronics and Electrical