Which parameter would you adjust to raise the baseline of a Doppler spectrum?

Which parameter would you adjust to raise the baseline of a Doppler spectrum?

• A. Increase the pulse repetition frequency
• B. Raise the zero baseline
• C. Increase the Doppler frequency
• D. Decrease the angle of incidence

Answer: (B)

Raising the baseline is about where zero velocity is shown on the display. The parameter that shifts this offset is the zero baseline setting; adjusting it moves the entire spectrum up or down, so the zero-velocity line sits higher on the display. This is a display offset, not a change to the actual flow or Doppler shift. Others affect the spectrum in different ways. Increasing the pulse repetition frequency changes how often you sample the signal and the Nyquist limit, but it doesn’t move the baseline. Increasing the Doppler frequency changes the amount of shift you observe, altering how far the spectrum spreads from zero rather than where zero sits. Decreasing the angle of incidence changes the measured velocity through the cos(theta) factor, again altering the scale of the spectrum rather than its vertical baseline.

Raising the baseline is about where zero velocity is shown on the display. The parameter that shifts this offset is the zero baseline setting; adjusting it moves the entire spectrum up or down, so the zero-velocity line sits higher on the display. This is a display offset, not a change to the actual flow or Doppler shift.

Others affect the spectrum in different ways. Increasing the pulse repetition frequency changes how often you sample the signal and the Nyquist limit, but it doesn’t move the baseline. Increasing the Doppler frequency changes the amount of shift you observe, altering how far the spectrum spreads from zero rather than where zero sits. Decreasing the angle of incidence changes the measured velocity through the cos(theta) factor, again altering the scale of the spectrum rather than its vertical baseline.