The FOI-2172 and FOI-2173 both provide complete electrical isolation for composite video and audio communications. The units are compatible with NTSC, PAL, and SECAM video broadcast standards. The units are transparent to all monochrome RS-170, color RS170A, and closed circuit RS-330 video. The FOI-2173 has an AGC (automatic gain control) to stabilize the video output for different fiber optic cable lengths. Adjusting the AGC potentiometer will also increase or decrease the overall scene brightness. The FOI-2172 can accept any level of audio input because clipping can be adjusted by the LVL potentiometer , while the FOI-2173 LVL potentiometer controls the volume.