Final answer:
The number of Doppler filters in a Primary Surveillance Radar system varies and is dependent on the specific radar system's design. Consultation of the system's technical documentation is required for an exact number.
Step-by-step explanation:
The number of Doppler filters in a Primary Surveillance Radar (PSR) can vary depending on the design and specifications of the particular radar system. However, most modern PSR systems use a bank of Doppler filters to analyze the frequency shift caused by the motion of reflective objects (such as aircraft) due to the Doppler effect. This helps in distinguishing moving targets from stationary ones and improving the detection and measurement of target speed. To provide a specific answer to the question, one would need to consult the technical documentation of the particular PSR system in question, as the number 8, 12, 16, or 20 could all be correct in different contexts. Without this specific information, it is not possible to definitively answer the question.