When conducting proof-of-performance (POP) testing, why is a bandpass filter necessary during the video signal to coherent beats test?

A bandpass filter is necessary during the video signal to coherent beats test mainly because it eliminates unwanted interference that could be generated by the spectrum analyzer itself. The spectrum analyzer typically covers a wide range of frequencies, and without the filter, extraneous signals can interfere with the measurement of the actual video signal. By using a bandpass filter, the testing focuses specifically on the frequency range of interest, ensuring that only relevant signals pass through for analysis. This enhances the accuracy and reliability of the proof-of-performance testing, allowing the technician to effectively evaluate the integrity of the video signal without the contamination of noise or interference from the equipment used in the measurement process. This step is crucial for maintaining high-quality signal integrity during testing.