Which parameter helps prevent aliasing by controlling the maximum detectable velocity?

Which parameter helps prevent aliasing by controlling the maximum detectable velocity?

• A. Threshold
• B. Gain
• C. PRF
• D. Angle correct

Answer: (C)

Aliasing in Doppler measurements happens when the Doppler frequency shift exceeds the Nyquist limit, which is half the pulse repetition frequency. The parameter that controls this limit is the pulse repetition frequency. By increasing PRF, you raise the Nyquist limit, so higher velocities can be detected without wraparound, effectively increasing the maximum detectable velocity and preventing aliasing. Note that the other options adjust signal strength or interpretation rather than the sampling rate: threshold (wall filter) removes very low velocities, gain amplifies the signal, and angle correction changes how velocity is calculated from the Doppler angle but doesn’t change the Nyquist limit.

Aliasing in Doppler measurements happens when the Doppler frequency shift exceeds the Nyquist limit, which is half the pulse repetition frequency. The parameter that controls this limit is the pulse repetition frequency. By increasing PRF, you raise the Nyquist limit, so higher velocities can be detected without wraparound, effectively increasing the maximum detectable velocity and preventing aliasing. Note that the other options adjust signal strength or interpretation rather than the sampling rate: threshold (wall filter) removes very low velocities, gain amplifies the signal, and angle correction changes how velocity is calculated from the Doppler angle but doesn’t change the Nyquist limit.