What is the effect of increasing the pulse repetition frequency (PRF) on Doppler measurements?

• A. Increases the risk of aliasing
• B. Reduces range ambiguity
• C. Decreases signal-to-noise ratio
• D. Has no effect

Answer: (B)

Increasing PRF means pulses are sent more often, so the Doppler signal is sampled more frequently. This tighter sampling reduces the chance that echoes from different depths get misassigned to the wrong range, helping to distinguish where the return came from. In Doppler terms, a higher PRF also raises the Nyquist limit, allowing higher Doppler shifts to be measured without aliasing, which improves the reliability of velocity measurements. Keep in mind, pushing PRF too high can limit the deepest depth you can sample because echoes must return before the next pulse, but within typical Doppler ranges, higher PRF reduces range ambiguity.