Doppler Shift Frequency to Voltage Conversion Techniques
Three methods of converting the Doppler signal to voltage proportional to mean velocity are compared. The traditional zero crosser is simple and reliable, however, erroneous readings are obtained in the presence of noise and broad band Doppler signals. The more complicated analog processor technique computes the true normalized first moment of the power spectrum and offers superior performance at low velocities and in the presence of noise. A new high frequency offset technique attempts to combine the simplicity of the zero crosser and the linearity of the analog processor. The signal is shifted to a high offset (100 KC typical) where the zero crossing rate becomes an excellent approximation to the first moment.