If a radar operator wants greater unambiguous range at the expense of velocity accuracy, which PRF setting should be used?

• A. Higher PRF.
• B. Lower PRF.
• C. Medium PRF.
• D. PRF does not affect unambiguous range.

Answer: (B)

Lower PRF is used when you want more unambiguous range, even if it means less accurate velocity. In pulsed radar, the maximum range over which returns can be assigned to a single transmitted pulse (unambiguous range) grows as PRF decreases, because the interval between pulses (PRI) is longer and the round-trip time can be larger without causing range ambiguity. The unambiguous range is proportional to c/(2PRF), so cutting PRF increases that range.

But Doppler (velocity) information relies on how often the radar samples the target’s motion per second. Fewer pulses per second mean fewer Doppler samples, reducing velocity resolution and the usable (Nyquist) velocity range. That’s the tradeoff: greater unambiguous range at the expense of velocity accuracy.