Final answer:
The receiver-exciter unit of an MSSR system develops the RF sample video for monitoring the radar signals.
Step-by-step explanation:
The part of the Monopulse Secondary Surveillance Radar (MSSR) system responsible for developing the radio frequency (RF) sample video for monitoring purposes is the receiver-exciter unit. This subassembly is designed to generate and amplify the RF signals before transmission, as well as to receive and process the reflected signals, or echoes, from the transponder-equipped aircraft. In the context of MSSR, the RF sample video is a key component that allows system operators and technicians to monitor the quality and integrity of the radar signals.