What parameter determines the maximum velocity that can be measured without aliasing?

What parameter determines the maximum velocity that can be measured without aliasing?

• A. Wall filter
• B. Gain
• C. Pulse repetition frequency
• D. Baseline

Answer: (C)

Aliasing in Doppler measurements is set by how often you sample the signal in time. The Doppler shift you can accurately capture must stay within ±half the pulse repetition frequency (the Nyquist limit). If the shift exceeds that limit, it wraps around and appears as a lower velocity, which is aliasing. Therefore, increasing the pulse repetition frequency raises the maximum velocity you can measure without aliasing, while decreasing it lowers that limit. The other controls (wall filter, gain, baseline) affect signal strength or display but do not change the sampling limit that governs aliasing. In short, the pulse repetition frequency determines the maximum unaliased velocity.

Aliasing in Doppler measurements is set by how often you sample the signal in time. The Doppler shift you can accurately capture must stay within ±half the pulse repetition frequency (the Nyquist limit). If the shift exceeds that limit, it wraps around and appears as a lower velocity, which is aliasing. Therefore, increasing the pulse repetition frequency raises the maximum velocity you can measure without aliasing, while decreasing it lowers that limit. The other controls (wall filter, gain, baseline) affect signal strength or display but do not change the sampling limit that governs aliasing. In short, the pulse repetition frequency determines the maximum unaliased velocity.